diff --git a/apps/components_tests/esm3/testsaveload.cpp b/apps/components_tests/esm3/testsaveload.cpp
index 7e5b73e4dd..0aac55d0fd 100644
--- a/apps/components_tests/esm3/testsaveload.cpp
+++ b/apps/components_tests/esm3/testsaveload.cpp
@@ -524,7 +524,7 @@ namespace ESM
             record.mData.mY = 2;
             record.mData.mZ = 3;
             record.mData.mDuration = 4;
-            record.mTargetActorId = 5;
+            record.mTargetActor = RefNum{ .mIndex = 5, .mContentFile = -1 };
             record.mTargetId = generateRandomRefId(32);
             record.mCellId = generateRandomString(257);
             record.mRemainingDuration = 6;
@@ -540,7 +540,10 @@ namespace ESM
                 EXPECT_EQ(result.mData.mDuration, record.mRemainingDuration);
             else
                 EXPECT_EQ(result.mData.mDuration, record.mData.mDuration);
-            EXPECT_EQ(result.mTargetActorId, record.mTargetActorId);
+            if (GetParam() > MaxActorIdSaveGameFormatVersion)
+            {
+                EXPECT_EQ(result.mTargetActor, record.mTargetActor);
+            }
             EXPECT_EQ(result.mTargetId, record.mTargetId);
             EXPECT_EQ(result.mCellId, record.mCellId);
             EXPECT_EQ(result.mRemainingDuration, record.mRemainingDuration);
diff --git a/apps/essimporter/converter.cpp b/apps/essimporter/converter.cpp
index 3e6b293f2c..b6ab2aeeb1 100644
--- a/apps/essimporter/converter.cpp
+++ b/apps/essimporter/converter.cpp
@@ -64,7 +64,7 @@ namespace
         refId = indexedRefId.substr(0, indexedRefId.size() - 8);
     }
 
-    int convertActorId(const std::string& indexedRefId, ESSImport::Context& context)
+    ESM::RefNum convertActorId(const std::string& indexedRefId, ESSImport::Context& context)
     {
         if (isIndexedRefId(indexedRefId))
         {
@@ -73,16 +73,15 @@ namespace
             splitIndexedRefId(indexedRefId, refIndex, refId);
 
             auto it = context.mActorIdMap.find(std::make_pair(refIndex, ESM::RefId::stringRefId(refId)));
-            if (it == context.mActorIdMap.end())
-                return -1;
-            return it->second;
+            if (it != context.mActorIdMap.end())
+                return it->second;
         }
         else if (indexedRefId == "PlayerSaveGame")
         {
-            return context.mPlayer.mObject.mCreatureStats.mActorId;
+            return context.mPlayer.mObject.mRef.mRefNum;
         }
 
-        return -1;
+        return {};
     }
 }
 
@@ -114,7 +113,7 @@ namespace ESSImport
         mGlobalMapImage->scaleImage(maph.size * 2, maph.size * 2, 1, GL_UNSIGNED_BYTE);
     }
 
-    void ConvertFMAP::write(ESM::ESMWriter& esm)
+    void ConvertFMAP::write(ESM::ESMWriter& esm) const
     {
         int numcells = mGlobalMapImage->s() / 18; // NB truncating, doesn't divide perfectly
                                                   // with the 512x512 map the game has by default
@@ -314,7 +313,7 @@ namespace ESSImport
             mIntCells[cell.mName] = std::move(newcell);
     }
 
-    void ConvertCell::writeCell(const Cell& cell, ESM::ESMWriter& esm)
+    void ConvertCell::writeCell(const Cell& cell, ESM::ESMWriter& esm) const
     {
         ESM::Cell esmcell = cell.mCell;
         esm.startRecord(ESM::REC_CSTA);
@@ -378,9 +377,8 @@ namespace ESSImport
                     convertNPCC(npccIt->second, objstate);
                     convertCellRef(cellref, objstate);
 
-                    objstate.mCreatureStats.mActorId = mContext->generateActorId();
-                    mContext->mActorIdMap.insert(
-                        std::make_pair(std::make_pair(refIndex, out.mRefID), objstate.mCreatureStats.mActorId));
+                    mContext->generateRefNum(objstate.mRef.mRefNum);
+                    mContext->mActorIdMap.emplace(std::make_pair(refIndex, out.mRefID), objstate.mRef.mRefNum);
 
                     esm.writeHNT("OBJE", ESM::REC_NPC_);
                     objstate.save(esm);
@@ -419,9 +417,8 @@ namespace ESSImport
                     convertCREC(crecIt->second, objstate);
                     convertCellRef(cellref, objstate);
 
-                    objstate.mCreatureStats.mActorId = mContext->generateActorId();
-                    mContext->mActorIdMap.insert(
-                        std::make_pair(std::make_pair(refIndex, out.mRefID), objstate.mCreatureStats.mActorId));
+                    mContext->generateRefNum(objstate.mRef.mRefNum);
+                    mContext->mActorIdMap.emplace(std::make_pair(refIndex, out.mRefID), objstate.mRef.mRefNum);
 
                     esm.writeHNT("OBJE", ESM::REC_CREA);
                     objstate.save(esm);
@@ -437,7 +434,7 @@ namespace ESSImport
         esm.endRecord(ESM::REC_CSTA);
     }
 
-    void ConvertCell::write(ESM::ESMWriter& esm)
+    void ConvertCell::write(ESM::ESMWriter& esm) const
     {
         for (const auto& cell : mIntCells)
             writeCell(cell.second, esm);
@@ -458,7 +455,7 @@ namespace ESSImport
         mProj.load(esm);
     }
 
-    void ConvertPROJ::write(ESM::ESMWriter& esm)
+    void ConvertPROJ::write(ESM::ESMWriter& esm) const
     {
         for (const PROJ::PNAM& pnam : mProj.mProjectiles)
         {
@@ -501,7 +498,7 @@ namespace ESSImport
         }
     }
 
-    void ConvertPROJ::convertBaseState(ESM::BaseProjectileState& base, const PROJ::PNAM& pnam)
+    void ConvertPROJ::convertBaseState(ESM::BaseProjectileState& base, const PROJ::PNAM& pnam) const
     {
         base.mId = ESM::RefId::stringRefId(pnam.mArrowId.toString());
         base.mPosition = pnam.mPosition;
@@ -510,7 +507,7 @@ namespace ESSImport
         orient.makeRotate(osg::Vec3f(0, 1, 0), pnam.mVelocity);
         base.mOrientation = orient;
 
-        base.mActorId = convertActorId(pnam.mActorId.toString(), *mContext);
+        base.mCaster = convertActorId(pnam.mActorId.toString(), *mContext);
     }
 
     void ConvertSPLM::read(ESM::ESMReader& esm)
@@ -519,7 +516,7 @@ namespace ESSImport
         mContext->mActiveSpells = mSPLM.mActiveSpells;
     }
 
-    void ConvertSPLM::write(ESM::ESMWriter& esm)
+    void ConvertSPLM::write(ESM::ESMWriter& esm) const
     {
         std::cerr << "Warning: Skipped active spell conversion (not implemented)" << std::endl;
     }
diff --git a/apps/essimporter/converter.hpp b/apps/essimporter/converter.hpp
index 9221adf83d..d819bf2374 100644
--- a/apps/essimporter/converter.hpp
+++ b/apps/essimporter/converter.hpp
@@ -54,7 +54,7 @@ namespace ESSImport
     {
     public:
         /// @return the order for writing this converter's records to the output file, in relation to other converters
-        virtual int getStage() { return 1; }
+        virtual int getStage() const { return 1; }
 
         virtual ~Converter() = default;
 
@@ -66,7 +66,7 @@ namespace ESSImport
 
         /// Called after the input file has been read in completely, which may be necessary
         /// if the conversion process relies on information in other records
-        virtual void write(ESM::ESMWriter& esm) {}
+        virtual void write(ESM::ESMWriter& esm) const {}
 
     protected:
         Context* mContext;
@@ -77,7 +77,7 @@ namespace ESSImport
     class DefaultConverter : public Converter
     {
     public:
-        int getStage() override { return 0; }
+        int getStage() const override { return 0; }
 
         void read(ESM::ESMReader& esm) override
         {
@@ -88,7 +88,7 @@ namespace ESSImport
             mRecords[record.mId] = record;
         }
 
-        void write(ESM::ESMWriter& esm) override
+        void write(ESM::ESMWriter& esm) const override
         {
             for (auto it = mRecords.begin(); it != mRecords.end(); ++it)
             {
@@ -257,7 +257,7 @@ namespace ESSImport
                 }
             }
         }
-        void write(ESM::ESMWriter& esm) override
+        void write(ESM::ESMWriter& esm) const override
         {
             esm.startRecord(ESM::REC_ASPL);
             esm.writeHNRefId("ID__", mSelectedSpell);
@@ -286,7 +286,7 @@ namespace ESSImport
             convertPCDT(pcdt, mContext->mPlayer, mContext->mDialogueState.mKnownTopics, mFirstPersonCam,
                 mTeleportingEnabled, mLevitationEnabled, mContext->mControlsState);
         }
-        void write(ESM::ESMWriter& esm) override
+        void write(ESM::ESMWriter& esm) const override
         {
             esm.startRecord(ESM::REC_ENAB);
             esm.writeHNT("TELE", mTeleportingEnabled);
@@ -331,7 +331,7 @@ namespace ESSImport
     {
     public:
         void read(ESM::ESMReader& esm) override;
-        void write(ESM::ESMWriter& esm) override;
+        void write(ESM::ESMWriter& esm) const override;
 
     private:
         osg::ref_ptr<osg::Image> mGlobalMapImage;
@@ -341,7 +341,7 @@ namespace ESSImport
     {
     public:
         void read(ESM::ESMReader& esm) override;
-        void write(ESM::ESMWriter& esm) override;
+        void write(ESM::ESMWriter& esm) const override;
 
     private:
         struct Cell
@@ -356,7 +356,7 @@ namespace ESSImport
 
         std::vector<ESM::CustomMarker> mMarkers;
 
-        void writeCell(const Cell& cell, ESM::ESMWriter& esm);
+        void writeCell(const Cell& cell, ESM::ESMWriter& esm) const;
     };
 
     class ConvertKLST : public Converter
@@ -371,7 +371,7 @@ namespace ESSImport
             mContext->mPlayer.mObject.mNpcStats.mWerewolfKills = klst.mWerewolfKills;
         }
 
-        void write(ESM::ESMWriter& esm) override
+        void write(ESM::ESMWriter& esm) const override
         {
             esm.startRecord(ESM::REC_DCOU);
             for (const auto& [id, count] : mKillCounter)
@@ -428,7 +428,7 @@ namespace ESSImport
                 }
             }
         }
-        void write(ESM::ESMWriter& esm) override
+        void write(ESM::ESMWriter& esm) const override
         {
             ESM::StolenItems items;
             for (auto it = mStolenItems.begin(); it != mStolenItems.end(); ++it)
@@ -486,7 +486,7 @@ namespace ESSImport
             if (dial.mIndex > 0)
                 mDials[id] = dial;
         }
-        void write(ESM::ESMWriter& esm) override
+        void write(ESM::ESMWriter& esm) const override
         {
             for (auto it = mDials.begin(); it != mDials.end(); ++it)
             {
@@ -539,7 +539,7 @@ namespace ESSImport
             mHasGame = true;
         }
 
-        int validateWeatherID(int weatherID)
+        int validateWeatherID(int weatherID) const
         {
             if (weatherID >= -1 && weatherID < 10)
             {
@@ -551,7 +551,7 @@ namespace ESSImport
             }
         }
 
-        void write(ESM::ESMWriter& esm) override
+        void write(ESM::ESMWriter& esm) const override
         {
             if (!mHasGame)
                 return;
@@ -586,7 +586,7 @@ namespace ESSImport
             convertSCPT(script, out);
             mScripts.push_back(std::move(out));
         }
-        void write(ESM::ESMWriter& esm) override
+        void write(ESM::ESMWriter& esm) const override
         {
             for (const auto& script : mScripts)
             {
@@ -604,12 +604,12 @@ namespace ESSImport
     class ConvertPROJ : public Converter
     {
     public:
-        int getStage() override { return 2; }
+        int getStage() const override { return 2; }
         void read(ESM::ESMReader& esm) override;
-        void write(ESM::ESMWriter& esm) override;
+        void write(ESM::ESMWriter& esm) const override;
 
     private:
-        void convertBaseState(ESM::BaseProjectileState& base, const PROJ::PNAM& pnam);
+        void convertBaseState(ESM::BaseProjectileState& base, const PROJ::PNAM& pnam) const;
         PROJ mProj;
     };
 
@@ -617,7 +617,7 @@ namespace ESSImport
     {
     public:
         void read(ESM::ESMReader& esm) override;
-        void write(ESM::ESMWriter& esm) override;
+        void write(ESM::ESMWriter& esm) const override;
 
     private:
         SPLM mSPLM;
diff --git a/apps/essimporter/importer.cpp b/apps/essimporter/importer.cpp
index 84ddfc0463..9bcc4466f1 100644
--- a/apps/essimporter/importer.cpp
+++ b/apps/essimporter/importer.cpp
@@ -388,13 +388,22 @@ namespace ESSImport
         profile.save(writer);
         writer.endRecord(ESM::REC_SAVE);
 
+        writer.startRecord(ESM::REC_DIAS);
+        context.mDialogueState.save(writer);
+        writer.endRecord(ESM::REC_DIAS);
+
+        writer.startRecord(ESM::REC_LUAM);
+        writer.writeHNT<double>("LUAW", 0);
+        writer.writeFormId(context.mNextRefNum, true);
+        writer.endRecord(ESM::REC_LUAM);
+
         // Writing order should be Dynamic Store -> Cells -> Player,
         // so that references to dynamic records can be recognized when loading
-        for (auto it = converters.begin(); it != converters.end(); ++it)
+        for (const auto& [_, converter] : converters)
         {
-            if (it->second->getStage() != 0)
+            if (converter->getStage() != 0)
                 continue;
-            it->second->write(writer);
+            converter->write(writer);
         }
 
         writer.startRecord(ESM::REC_NPC_);
@@ -402,11 +411,11 @@ namespace ESSImport
         context.mPlayerBase.save(writer);
         writer.endRecord(ESM::REC_NPC_);
 
-        for (auto it = converters.begin(); it != converters.end(); ++it)
+        for (const auto& [_, converter] : converters)
         {
-            if (it->second->getStage() != 1)
+            if (converter->getStage() != 1)
                 continue;
-            it->second->write(writer);
+            converter->write(writer);
         }
 
         writer.startRecord(ESM::REC_PLAY);
@@ -418,22 +427,14 @@ namespace ESSImport
         context.mPlayer.save(writer);
         writer.endRecord(ESM::REC_PLAY);
 
-        writer.startRecord(ESM::REC_ACTC);
-        writer.writeHNT("COUN", context.mNextActorId);
-        writer.endRecord(ESM::REC_ACTC);
-
         // Stage 2 requires cell references to be written / actors IDs assigned
-        for (auto it = converters.begin(); it != converters.end(); ++it)
+        for (const auto& [_, converter] : converters)
         {
-            if (it->second->getStage() != 2)
+            if (converter->getStage() != 2)
                 continue;
-            it->second->write(writer);
+            converter->write(writer);
         }
 
-        writer.startRecord(ESM::REC_DIAS);
-        context.mDialogueState.save(writer);
-        writer.endRecord(ESM::REC_DIAS);
-
         writer.startRecord(ESM::REC_INPU);
         context.mControlsState.save(writer);
         writer.endRecord(ESM::REC_INPU);
diff --git a/apps/essimporter/importercontext.hpp b/apps/essimporter/importercontext.hpp
index 03ea9d0943..ac54b7d5be 100644
--- a/apps/essimporter/importercontext.hpp
+++ b/apps/essimporter/importercontext.hpp
@@ -45,8 +45,8 @@ namespace ESSImport
         std::map<std::pair<int, ESM::RefId>, NPCC> mNpcChanges;
         std::map<std::pair<int, ESM::RefId>, CNTC> mContainerChanges;
 
-        std::map<std::pair<int, ESM::RefId>, int> mActorIdMap;
-        int mNextActorId;
+        std::map<std::pair<int, ESM::RefId>, ESM::RefNum> mActorIdMap;
+        ESM::RefNum mNextRefNum;
 
         std::map<ESM::RefId, ESM::Creature> mCreatures;
         std::map<ESM::RefId, ESM::NPC> mNpcs;
@@ -58,7 +58,6 @@ namespace ESSImport
             , mMonth(0)
             , mYear(0)
             , mHour(0.f)
-            , mNextActorId(0)
         {
             mPlayer.mCellId = ESM::RefId::esm3ExteriorCell(0, 0);
             mPlayer.mLastKnownExteriorPosition[0] = mPlayer.mLastKnownExteriorPosition[1]
@@ -69,7 +68,7 @@ namespace ESSImport
             mPlayer.mObject.blank();
             mPlayer.mObject.mEnabled = true;
             mPlayer.mObject.mRef.mRefID = ESM::RefId::stringRefId("player"); // REFR.mRefID would be PlayerSaveGame
-            mPlayer.mObject.mCreatureStats.mActorId = generateActorId();
+            generateRefNum(mPlayer.mObject.mRef.mRefNum);
 
             mGlobalMapState.mBounds.mMinX = 0;
             mGlobalMapState.mBounds.mMaxX = 0;
@@ -79,7 +78,16 @@ namespace ESSImport
             mPlayerBase.blank();
         }
 
-        int generateActorId() { return mNextActorId++; }
+        void generateRefNum(ESM::RefNum& refNum)
+        {
+            if (!refNum.isSet())
+            {
+                mNextRefNum.mIndex++;
+                if (mNextRefNum.mIndex == 0)
+                    mNextRefNum.mContentFile--;
+                refNum = mNextRefNum;
+            }
+        }
     };
 
 }
diff --git a/apps/openmw/mwbase/mechanicsmanager.hpp b/apps/openmw/mwbase/mechanicsmanager.hpp
index 22eaad8dc1..c363c2b808 100644
--- a/apps/openmw/mwbase/mechanicsmanager.hpp
+++ b/apps/openmw/mwbase/mechanicsmanager.hpp
@@ -294,7 +294,7 @@ namespace MWBase
         /// It only applies to the current form the NPC is in.
         virtual void applyWerewolfAcrobatics(const MWWorld::Ptr& actor) = 0;
 
-        virtual void cleanupSummonedCreature(const MWWorld::Ptr& caster, int creatureActorId) = 0;
+        virtual void cleanupSummonedCreature(ESM::RefNum creature) = 0;
 
         virtual void confiscateStolenItemToOwner(
             const MWWorld::Ptr& player, const MWWorld::Ptr& item, const MWWorld::Ptr& victim, int count)
diff --git a/apps/openmw/mwbase/world.hpp b/apps/openmw/mwbase/world.hpp
index 23fb98063f..819c4ac91d 100644
--- a/apps/openmw/mwbase/world.hpp
+++ b/apps/openmw/mwbase/world.hpp
@@ -196,9 +196,6 @@ namespace MWBase
         ///< Return a pointer to a liveCellRef with the given name.
         /// \param activeOnly do non search inactive cells.
 
-        virtual MWWorld::Ptr searchPtrViaActorId(int actorId) = 0;
-        ///< Search is limited to the active cells.
-
         virtual MWWorld::Ptr findContainer(const MWWorld::ConstPtr& ptr) = 0;
         ///< Return a pointer to a liveCellRef which contains \a ptr.
         /// \note Search is limited to the active cells.
@@ -375,7 +372,7 @@ namespace MWBase
         virtual void applyDeferredPreviewRotationToPlayer(float dt) = 0;
         virtual void disableDeferredPreviewRotation() = 0;
 
-        virtual void saveLoaded() = 0;
+        virtual void saveLoaded(const ESM::ESMReader& reader) = 0;
 
         virtual void setupPlayer() = 0;
         virtual void renderPlayer() = 0;
diff --git a/apps/openmw/mwclass/creature.cpp b/apps/openmw/mwclass/creature.cpp
index c2c930ce1b..7effead29f 100644
--- a/apps/openmw/mwclass/creature.cpp
+++ b/apps/openmw/mwclass/creature.cpp
@@ -376,14 +376,14 @@ namespace MWClass
         {
             MWMechanics::CreatureStats& statsAttacker = attacker.getClass().getCreatureStats(attacker);
             // First handle the attacked actor
-            if ((stats.getHitAttemptActorId() == -1)
+            if (!stats.getHitAttemptActor().isSet()
                 && (statsAttacker.getAiSequence().isInCombat(ptr) || attacker == MWMechanics::getPlayer()))
-                stats.setHitAttemptActorId(statsAttacker.getActorId());
+                stats.setHitAttemptActor(attacker.getCellRef().getRefNum());
 
             // Next handle the attacking actor
-            if ((statsAttacker.getHitAttemptActorId() == -1)
+            if (!statsAttacker.getHitAttemptActor().isSet()
                 && (statsAttacker.getAiSequence().isInCombat(ptr) || attacker == MWMechanics::getPlayer()))
-                statsAttacker.setHitAttemptActorId(stats.getActorId());
+                statsAttacker.setHitAttemptActor(ptr.getCellRef().getRefNum());
         }
 
         if (!object.empty())
diff --git a/apps/openmw/mwclass/creaturelevlist.cpp b/apps/openmw/mwclass/creaturelevlist.cpp
index f16601531d..15a73fbf1d 100644
--- a/apps/openmw/mwclass/creaturelevlist.cpp
+++ b/apps/openmw/mwclass/creaturelevlist.cpp
@@ -1,5 +1,6 @@
 #include "creaturelevlist.hpp"
 
+#include <components/esm3/actoridconverter.hpp>
 #include <components/esm3/creaturelevliststate.hpp>
 #include <components/esm3/loadlevlist.hpp>
 
@@ -9,6 +10,7 @@
 #include "../mwworld/customdata.hpp"
 #include "../mwworld/esmstore.hpp"
 #include "../mwworld/manualref.hpp"
+#include "../mwworld/worldmodel.hpp"
 
 #include "../mwmechanics/creaturestats.hpp"
 
@@ -20,9 +22,15 @@ namespace MWClass
     class CreatureLevListCustomData : public MWWorld::TypedCustomData<CreatureLevListCustomData>
     {
     public:
-        // actorId of the creature we spawned
-        int mSpawnActorId;
-        bool mSpawn; // Should a new creature be spawned?
+        ESM::RefNum mSpawnedActor;
+        bool mSpawn = true; // Should a new creature be spawned?
+
+        MWWorld::Ptr getSpawnedPtr() const
+        {
+            if (mSpawnedActor.isSet())
+                return MWBase::Environment::get().getWorldModel()->getPtr(mSpawnedActor);
+            return {};
+        }
 
         CreatureLevListCustomData& asCreatureLevListCustomData() override { return *this; }
         const CreatureLevListCustomData& asCreatureLevListCustomData() const override { return *this; }
@@ -46,9 +54,7 @@ namespace MWClass
             return;
 
         CreatureLevListCustomData& customData = ptr.getRefData().getCustomData()->asCreatureLevListCustomData();
-        MWWorld::Ptr creature = (customData.mSpawnActorId == -1)
-            ? MWWorld::Ptr()
-            : MWBase::Environment::get().getWorld()->searchPtrViaActorId(customData.mSpawnActorId);
+        MWWorld::Ptr creature = customData.getSpawnedPtr();
         if (!creature.isEmpty())
             MWBase::Environment::get().getWorld()->adjustPosition(creature, force);
     }
@@ -71,13 +77,7 @@ namespace MWClass
         if (customData.mSpawn)
             return;
 
-        MWWorld::Ptr creature;
-        if (customData.mSpawnActorId != -1)
-        {
-            creature = MWBase::Environment::get().getWorld()->searchPtrViaActorId(customData.mSpawnActorId);
-            if (creature.isEmpty())
-                creature = ptr.getCell()->getMovedActor(customData.mSpawnActorId);
-        }
+        MWWorld::Ptr creature = customData.getSpawnedPtr();
         if (!creature.isEmpty())
         {
             const MWMechanics::CreatureStats& creatureStats = creature.getClass().getCreatureStats(creature);
@@ -116,21 +116,17 @@ namespace MWClass
         if (!id.empty())
         {
             // Delete the previous creature
-            if (customData.mSpawnActorId != -1)
-            {
-                MWWorld::Ptr creature
-                    = MWBase::Environment::get().getWorld()->searchPtrViaActorId(customData.mSpawnActorId);
-                if (!creature.isEmpty())
-                    MWBase::Environment::get().getWorld()->deleteObject(creature);
-                customData.mSpawnActorId = -1;
-            }
+            MWWorld::Ptr previous = customData.getSpawnedPtr();
+            if (!previous.isEmpty())
+                MWBase::Environment::get().getWorld()->deleteObject(previous);
 
             MWWorld::ManualRef manualRef(store, id);
             manualRef.getPtr().getCellRef().setPosition(ptr.getCellRef().getPosition());
             manualRef.getPtr().getCellRef().setScale(ptr.getCellRef().getScale());
             MWWorld::Ptr placed = MWBase::Environment::get().getWorld()->placeObject(
                 manualRef.getPtr(), ptr.getCell(), ptr.getRefData().getPosition());
-            customData.mSpawnActorId = placed.getClass().getCreatureStats(placed).getActorId();
+            MWBase::Environment::get().getWorldModel()->registerPtr(placed);
+            customData.mSpawnedActor = placed.getCellRef().getRefNum();
             customData.mSpawn = false;
         }
         else
@@ -141,11 +137,7 @@ namespace MWClass
     {
         if (!ptr.getRefData().getCustomData())
         {
-            std::unique_ptr<CreatureLevListCustomData> data = std::make_unique<CreatureLevListCustomData>();
-            data->mSpawnActorId = -1;
-            data->mSpawn = true;
-
-            ptr.getRefData().setCustomData(std::move(data));
+            ptr.getRefData().setCustomData(std::make_unique<CreatureLevListCustomData>());
         }
     }
 
@@ -157,8 +149,10 @@ namespace MWClass
         ensureCustomData(ptr);
         CreatureLevListCustomData& customData = ptr.getRefData().getCustomData()->asCreatureLevListCustomData();
         const ESM::CreatureLevListState& levListState = state.asCreatureLevListState();
-        customData.mSpawnActorId = levListState.mSpawnActorId;
+        customData.mSpawnedActor = levListState.mSpawnedActor;
         customData.mSpawn = levListState.mSpawn;
+        if (state.mActorIdConverter)
+            state.mActorIdConverter->convert(customData.mSpawnedActor, customData.mSpawnedActor.mIndex);
     }
 
     void CreatureLevList::writeAdditionalState(const MWWorld::ConstPtr& ptr, ESM::ObjectState& state) const
@@ -171,7 +165,7 @@ namespace MWClass
 
         const CreatureLevListCustomData& customData = ptr.getRefData().getCustomData()->asCreatureLevListCustomData();
         ESM::CreatureLevListState& levListState = state.asCreatureLevListState();
-        levListState.mSpawnActorId = customData.mSpawnActorId;
+        levListState.mSpawnedActor = customData.mSpawnedActor;
         levListState.mSpawn = customData.mSpawn;
     }
 }
diff --git a/apps/openmw/mwclass/npc.cpp b/apps/openmw/mwclass/npc.cpp
index fd62765e61..7af84d1a48 100644
--- a/apps/openmw/mwclass/npc.cpp
+++ b/apps/openmw/mwclass/npc.cpp
@@ -728,14 +728,14 @@ namespace MWClass
         {
             MWMechanics::CreatureStats& statsAttacker = attacker.getClass().getCreatureStats(attacker);
             // First handle the attacked actor
-            if ((stats.getHitAttemptActorId() == -1)
+            if (!stats.getHitAttemptActor().isSet()
                 && (statsAttacker.getAiSequence().isInCombat(ptr) || attacker == MWMechanics::getPlayer()))
-                stats.setHitAttemptActorId(statsAttacker.getActorId());
+                stats.setHitAttemptActor(attacker.getCellRef().getRefNum());
 
             // Next handle the attacking actor
-            if ((statsAttacker.getHitAttemptActorId() == -1)
+            if (!statsAttacker.getHitAttemptActor().isSet()
                 && (statsAttacker.getAiSequence().isInCombat(ptr) || attacker == MWMechanics::getPlayer()))
-                statsAttacker.setHitAttemptActorId(stats.getActorId());
+                statsAttacker.setHitAttemptActor(ptr.getCellRef().getRefNum());
         }
 
         if (!object.empty())
diff --git a/apps/openmw/mwgui/container.cpp b/apps/openmw/mwgui/container.cpp
index 1b6dd4cbfb..bb8ccc5536 100644
--- a/apps/openmw/mwgui/container.cpp
+++ b/apps/openmw/mwgui/container.cpp
@@ -312,7 +312,7 @@ namespace MWGui
                     // Clean up summoned creatures as well
                     auto& creatureMap = creatureStats.getSummonedCreatureMap();
                     for (const auto& creature : creatureMap)
-                        MWBase::Environment::get().getMechanicsManager()->cleanupSummonedCreature(ptr, creature.second);
+                        MWBase::Environment::get().getMechanicsManager()->cleanupSummonedCreature(creature.second);
                     creatureMap.clear();
 
                     // Check if we are a summon and inform our master we've bit the dust
@@ -323,7 +323,7 @@ namespace MWGui
                             const auto& summoner = package->getTarget();
                             auto& summons = summoner.getClass().getCreatureStats(summoner).getSummonedCreatureMap();
                             auto it = std::find_if(summons.begin(), summons.end(),
-                                [&](const auto& entry) { return entry.second == creatureStats.getActorId(); });
+                                [&](const auto& entry) { return entry.second == ptr.getCellRef().getRefNum(); });
                             if (it != summons.end())
                             {
                                 auto summon = *it;
diff --git a/apps/openmw/mwgui/hud.cpp b/apps/openmw/mwgui/hud.cpp
index fbd4dff33b..53cfd89f5b 100644
--- a/apps/openmw/mwgui/hud.cpp
+++ b/apps/openmw/mwgui/hud.cpp
@@ -19,6 +19,7 @@
 
 #include "../mwworld/class.hpp"
 #include "../mwworld/esmstore.hpp"
+#include "../mwworld/worldmodel.hpp"
 
 #include "../mwmechanics/actorutil.hpp"
 #include "../mwmechanics/npcstats.hpp"
@@ -34,36 +35,7 @@ namespace MWGui
     HUD::HUD(CustomMarkerCollection& customMarkers, DragAndDrop* dragAndDrop, MWRender::LocalMap* localMapRender)
         : WindowBase("openmw_hud.layout")
         , LocalMapBase(customMarkers, localMapRender, Settings::map().mLocalMapHudFogOfWar)
-        , mHealth(nullptr)
-        , mMagicka(nullptr)
-        , mStamina(nullptr)
-        , mDrowning(nullptr)
-        , mWeapImage(nullptr)
-        , mSpellImage(nullptr)
-        , mWeapStatus(nullptr)
-        , mSpellStatus(nullptr)
-        , mEffectBox(nullptr)
-        , mMinimap(nullptr)
-        , mCrosshair(nullptr)
-        , mCellNameBox(nullptr)
-        , mDrowningBar(nullptr)
-        , mDrowningFlash(nullptr)
-        , mHealthManaStaminaBaseLeft(0)
-        , mWeapBoxBaseLeft(0)
-        , mSpellBoxBaseLeft(0)
-        , mMinimapBoxBaseRight(0)
-        , mEffectBoxBaseRight(0)
         , mDragAndDrop(dragAndDrop)
-        , mCellNameTimer(0.0f)
-        , mWeaponSpellTimer(0.f)
-        , mMapVisible(true)
-        , mWeaponVisible(true)
-        , mSpellVisible(true)
-        , mWorldMouseOver(false)
-        , mEnemyActorId(-1)
-        , mEnemyHealthTimer(-1)
-        , mIsDrowning(false)
-        , mDrowningFlashTheta(0.f)
     {
         // Energy bars
         getWidget(mHealthFrame, "HealthFrame");
@@ -338,7 +310,7 @@ namespace MWGui
 
         mSpellIcons->updateWidgets(mEffectBox, true);
 
-        if (mEnemyActorId != -1 && mEnemyHealth->getVisible())
+        if (mEnemyActor.isSet() && mEnemyHealth->getVisible())
         {
             updateEnemyHealthBar();
         }
@@ -579,7 +551,7 @@ namespace MWGui
 
     void HUD::updateEnemyHealthBar()
     {
-        MWWorld::Ptr enemy = MWBase::Environment::get().getWorld()->searchPtrViaActorId(mEnemyActorId);
+        MWWorld::Ptr enemy = MWBase::Environment::get().getWorldModel()->getPtr(mEnemyActor);
         if (enemy.isEmpty())
             return;
         MWMechanics::CreatureStats& stats = enemy.getClass().getCreatureStats(enemy);
@@ -599,7 +571,7 @@ namespace MWGui
 
     void HUD::setEnemy(const MWWorld::Ptr& enemy)
     {
-        mEnemyActorId = enemy.getClass().getCreatureStats(enemy).getActorId();
+        mEnemyActor = enemy.getCellRef().getRefNum();
         mEnemyHealthTimer = MWBase::Environment::get()
                                 .getESMStore()
                                 ->get<ESM::GameSetting>()
@@ -613,12 +585,12 @@ namespace MWGui
 
     void HUD::clear()
     {
-        mEnemyActorId = -1;
+        mEnemyActor = {};
         mEnemyHealthTimer = -1;
 
         mWeaponSpellTimer = 0.f;
-        mWeaponName = std::string();
-        mSpellName = std::string();
+        mWeaponName.clear();
+        mSpellName.clear();
         mWeaponSpellBox->setVisible(false);
 
         mWeapStatus->setProgressRange(100);
diff --git a/apps/openmw/mwgui/hud.hpp b/apps/openmw/mwgui/hud.hpp
index 9e9fa4e597..ef71551965 100644
--- a/apps/openmw/mwgui/hud.hpp
+++ b/apps/openmw/mwgui/hud.hpp
@@ -64,47 +64,42 @@ namespace MWGui
         void dropDraggedItem(float mouseX, float mouseY);
 
     private:
-        MyGUI::ProgressBar *mHealth, *mMagicka, *mStamina, *mEnemyHealth, *mDrowning;
-        MyGUI::Widget* mHealthFrame;
-        MyGUI::Widget *mWeapBox, *mSpellBox, *mSneakBox;
-        ItemWidget* mWeapImage;
-        SpellWidget* mSpellImage;
-        MyGUI::ProgressBar *mWeapStatus, *mSpellStatus;
-        MyGUI::Widget *mEffectBox, *mMinimapBox;
-        MyGUI::Button* mMinimapButton;
-        MyGUI::ScrollView* mMinimap;
-        MyGUI::ImageBox* mCrosshair;
-        MyGUI::TextBox* mCellNameBox;
-        MyGUI::TextBox* mWeaponSpellBox;
-        MyGUI::Widget *mDrowningBar, *mDrowningFrame, *mDrowningFlash;
+        MyGUI::ProgressBar *mHealth = nullptr, *mMagicka = nullptr, *mStamina = nullptr, *mEnemyHealth = nullptr,
+                           *mDrowning = nullptr;
+        MyGUI::Widget* mHealthFrame = nullptr;
+        MyGUI::Widget *mWeapBox = nullptr, *mSpellBox = nullptr, *mSneakBox = nullptr;
+        ItemWidget* mWeapImage = nullptr;
+        SpellWidget* mSpellImage = nullptr;
+        MyGUI::ProgressBar *mWeapStatus = nullptr, *mSpellStatus = nullptr;
+        MyGUI::Widget *mEffectBox = nullptr, *mMinimapBox = nullptr;
+        MyGUI::Button* mMinimapButton = nullptr;
+        MyGUI::ScrollView* mMinimap = nullptr;
+        MyGUI::ImageBox* mCrosshair = nullptr;
+        MyGUI::TextBox* mCellNameBox = nullptr;
+        MyGUI::TextBox* mWeaponSpellBox = nullptr;
+        MyGUI::Widget *mDrowningBar = nullptr, *mDrowningFrame = nullptr, *mDrowningFlash = nullptr;
+        DragAndDrop* mDragAndDrop;
+        std::string mCellName;
+        std::string mWeaponName;
+        std::string mSpellName;
+        std::unique_ptr<SpellIcons> mSpellIcons;
+        ESM::RefNum mEnemyActor;
 
         // bottom left elements
         int mHealthManaStaminaBaseLeft, mWeapBoxBaseLeft, mSpellBoxBaseLeft, mSneakBoxBaseLeft;
         // bottom right elements
         int mMinimapBoxBaseRight, mEffectBoxBaseRight;
 
-        DragAndDrop* mDragAndDrop;
+        float mCellNameTimer = 0.f;
+        float mWeaponSpellTimer = 0.f;
+        float mEnemyHealthTimer = -1;
+        float mDrowningFlashTheta = 0.f;
 
-        std::string mCellName;
-        float mCellNameTimer;
-
-        std::string mWeaponName;
-        std::string mSpellName;
-        float mWeaponSpellTimer;
-
-        bool mMapVisible;
-        bool mWeaponVisible;
-        bool mSpellVisible;
-
-        bool mWorldMouseOver;
-
-        std::unique_ptr<SpellIcons> mSpellIcons;
-
-        int mEnemyActorId;
-        float mEnemyHealthTimer;
-
-        bool mIsDrowning;
-        float mDrowningFlashTheta;
+        bool mMapVisible = true;
+        bool mWeaponVisible = true;
+        bool mSpellVisible = true;
+        bool mWorldMouseOver = false;
+        bool mIsDrowning = false;
 
         void onWorldClicked(MyGUI::Widget* sender);
         void onWorldMouseOver(MyGUI::Widget* sender, int x, int y);
diff --git a/apps/openmw/mwlua/localscripts.cpp b/apps/openmw/mwlua/localscripts.cpp
index 99c994304b..d9834abd91 100644
--- a/apps/openmw/mwlua/localscripts.cpp
+++ b/apps/openmw/mwlua/localscripts.cpp
@@ -170,34 +170,25 @@ namespace MWLua
                                         float duration, const osg::Vec3f& dest, bool repeat, bool cancelOther) {
             const MWWorld::Ptr& ptr = self.ptr();
             MWMechanics::AiSequence& ai = ptr.getClass().getCreatureStats(ptr).getAiSequence();
+            std::string_view cellNameId;
             if (cell)
-            {
-                ai.stack(MWMechanics::AiFollow(target.ptr().getCellRef().getRefId(),
-                             cell->mStore->getCell()->getNameId(), duration, dest.x(), dest.y(), dest.z(), repeat),
-                    ptr, cancelOther);
-            }
-            else
-            {
-                ai.stack(MWMechanics::AiFollow(
-                             target.ptr().getCellRef().getRefId(), duration, dest.x(), dest.y(), dest.z(), repeat),
-                    ptr, cancelOther);
-            }
+                cellNameId = cell->mStore->getCell()->getNameId();
+            ai.stack(
+                MWMechanics::AiFollow(getId(target.ptr()), cellNameId, duration, dest.x(), dest.y(), dest.z(), repeat),
+                ptr, cancelOther);
         };
         selfAPI["_startAiEscort"] = [](SelfObject& self, const LObject& target, LCell cell, float duration,
                                         const osg::Vec3f& dest, bool repeat, bool cancelOther) {
             const MWWorld::Ptr& ptr = self.ptr();
             MWMechanics::AiSequence& ai = ptr.getClass().getCreatureStats(ptr).getAiSequence();
-            // TODO: change AiEscort implementation to accept ptr instead of a non-unique refId.
-            const ESM::RefId& refId = target.ptr().getCellRef().getRefId();
             int gameHoursDuration = static_cast<int>(std::ceil(duration / 3600.0));
             auto* esmCell = cell.mStore->getCell();
-            if (esmCell->isExterior())
-                ai.stack(MWMechanics::AiEscort(refId, gameHoursDuration, dest.x(), dest.y(), dest.z(), repeat), ptr,
-                    cancelOther);
-            else
-                ai.stack(MWMechanics::AiEscort(
-                             refId, esmCell->getNameId(), gameHoursDuration, dest.x(), dest.y(), dest.z(), repeat),
-                    ptr, cancelOther);
+            std::string_view cellNameId;
+            if (!esmCell->isExterior())
+                cellNameId = esmCell->getNameId();
+            ai.stack(MWMechanics::AiEscort(
+                         getId(target.ptr()), cellNameId, gameHoursDuration, dest.x(), dest.y(), dest.z(), repeat),
+                ptr, cancelOther);
         };
         selfAPI["_startAiWander"]
             = [](SelfObject& self, int distance, int duration, sol::table luaIdle, bool repeat, bool cancelOther) {
diff --git a/apps/openmw/mwlua/magicbindings.cpp b/apps/openmw/mwlua/magicbindings.cpp
index d36b31a931..97cf4dfb89 100644
--- a/apps/openmw/mwlua/magicbindings.cpp
+++ b/apps/openmw/mwlua/magicbindings.cpp
@@ -546,8 +546,7 @@ namespace MWLua
               });
         activeSpellT["caster"]
             = sol::readonly_property([lua = state.lua_state()](const ActiveSpell& activeSpell) -> sol::object {
-                  auto caster = MWBase::Environment::get().getWorld()->searchPtrViaActorId(
-                      activeSpell.mParams.getCasterActorId());
+                  auto caster = MWBase::Environment::get().getWorldModel()->getPtr(activeSpell.mParams.getCaster());
                   if (caster.isEmpty())
                       return sol::nil;
                   else
diff --git a/apps/openmw/mwmechanics/activespells.cpp b/apps/openmw/mwmechanics/activespells.cpp
index 109b75e1d4..d2f4e7d2d4 100644
--- a/apps/openmw/mwmechanics/activespells.cpp
+++ b/apps/openmw/mwmechanics/activespells.cpp
@@ -9,6 +9,7 @@
 #include <components/misc/strings/algorithm.hpp>
 
 #include <components/esm/generatedrefid.hpp>
+#include <components/esm3/actoridconverter.hpp>
 #include <components/esm3/loadench.hpp>
 #include <components/esm3/loadmgef.hpp>
 #include <components/esm3/loadstat.hpp>
@@ -30,6 +31,7 @@
 #include "../mwworld/esmstore.hpp"
 #include "../mwworld/inventorystore.hpp"
 #include "../mwworld/manualref.hpp"
+#include "../mwworld/worldmodel.hpp"
 
 namespace
 {
@@ -103,20 +105,19 @@ namespace MWMechanics
         const MWWorld::Ptr& caster, const ESM::RefId& id, std::string_view sourceName, ESM::RefNum item)
         : mSourceSpellId(id)
         , mDisplayName(sourceName)
-        , mCasterActorId(-1)
         , mItem(item)
         , mFlags()
         , mWorsenings(-1)
     {
         if (!caster.isEmpty() && caster.getClass().isActor())
-            mCasterActorId = caster.getClass().getCreatureStats(caster).getActorId();
+            mCaster = caster.getCellRef().getRefNum();
     }
 
     ActiveSpells::ActiveSpellParams::ActiveSpellParams(
         const ESM::Spell* spell, const MWWorld::Ptr& actor, bool ignoreResistances)
         : mSourceSpellId(spell->mId)
         , mDisplayName(spell->mName)
-        , mCasterActorId(actor.getClass().getCreatureStats(actor).getActorId())
+        , mCaster(actor.getCellRef().getRefNum())
         , mFlags()
         , mWorsenings(-1)
     {
@@ -131,7 +132,7 @@ namespace MWMechanics
         const MWWorld::ConstPtr& item, const ESM::Enchantment* enchantment, const MWWorld::Ptr& actor)
         : mSourceSpellId(item.getCellRef().getRefId())
         , mDisplayName(item.getClass().getName(item))
-        , mCasterActorId(actor.getClass().getCreatureStats(actor).getActorId())
+        , mCaster(actor.getCellRef().getRefNum())
         , mItem(item.getCellRef().getRefNum())
         , mFlags()
         , mWorsenings(-1)
@@ -146,7 +147,7 @@ namespace MWMechanics
         , mSourceSpellId(params.mSourceSpellId)
         , mEffects(params.mEffects)
         , mDisplayName(params.mDisplayName)
-        , mCasterActorId(params.mCasterActorId)
+        , mCaster(params.mCaster)
         , mItem(params.mItem)
         , mFlags(params.mFlags)
         , mWorsenings(params.mWorsenings)
@@ -157,7 +158,7 @@ namespace MWMechanics
     ActiveSpells::ActiveSpellParams::ActiveSpellParams(const ActiveSpellParams& params, const MWWorld::Ptr& actor)
         : mSourceSpellId(params.mSourceSpellId)
         , mDisplayName(params.mDisplayName)
-        , mCasterActorId(actor.getClass().getCreatureStats(actor).getActorId())
+        , mCaster(actor.getCellRef().getRefNum())
         , mItem(params.mItem)
         , mFlags(params.mFlags)
         , mWorsenings(-1)
@@ -171,7 +172,7 @@ namespace MWMechanics
         params.mSourceSpellId = mSourceSpellId;
         params.mEffects = mEffects;
         params.mDisplayName = mDisplayName;
-        params.mCasterActorId = mCasterActorId;
+        params.mCaster = mCaster;
         params.mItem = mItem;
         params.mFlags = mFlags;
         params.mWorsenings = mWorsenings;
@@ -375,8 +376,7 @@ namespace MWMechanics
     bool ActiveSpells::updateActiveSpell(
         const MWWorld::Ptr& ptr, float duration, Collection::iterator& spellIt, UpdateContext& context)
     {
-        const auto caster = MWBase::Environment::get().getWorld()->searchPtrViaActorId(
-            spellIt->mCasterActorId); // Maybe make this search outside active grid?
+        const auto caster = MWBase::Environment::get().getWorldModel()->getPtr(spellIt->mCaster);
         bool removedSpell = false;
         std::optional<ActiveSpellParams> reflected;
         for (auto it = spellIt->mEffects.begin(); it != spellIt->mEffects.end();)
@@ -484,8 +484,8 @@ namespace MWMechanics
         if (!spell.hasFlag(ESM::ActiveSpells::Flag_Stackable))
         {
             auto found = std::find_if(mSpells.begin(), mSpells.end(), [&](const auto& existing) {
-                return spell.mSourceSpellId == existing.mSourceSpellId
-                    && spell.mCasterActorId == existing.mCasterActorId && spell.mItem == existing.mItem;
+                return spell.mSourceSpellId == existing.mSourceSpellId && spell.mCaster == existing.mCaster
+                    && spell.mItem == existing.mItem;
             });
             if (found != mSpells.end())
             {
@@ -659,9 +659,9 @@ namespace MWMechanics
             ptr);
     }
 
-    void ActiveSpells::purge(const MWWorld::Ptr& ptr, int casterActorId)
+    void ActiveSpells::purge(const MWWorld::Ptr& ptr, ESM::RefNum actor)
     {
-        purge([=](const ActiveSpellParams& params) { return params.mCasterActorId == casterActorId; }, ptr);
+        purge([=](const ActiveSpellParams& params) { return params.mCaster == actor; }, ptr);
     }
 
     void ActiveSpells::clear(const MWWorld::Ptr& ptr)
@@ -698,6 +698,22 @@ namespace MWMechanics
         }
         for (const ESM::ActiveSpells::ActiveSpellParams& spell : state.mQueue)
             mQueue.emplace_back(ActiveSpellParams{ spell });
+        if (state.mActorIdConverter)
+        {
+            const auto convertSummons = [converter = state.mActorIdConverter](auto& collection) {
+                for (ActiveSpellParams& params : collection)
+                {
+                    converter->convert(params.mCaster, params.mCaster.mIndex);
+                    for (ESM::ActiveEffect& effect : params.mEffects)
+                    {
+                        if (ESM::RefNum* refNum = std::get_if<ESM::RefNum>(&effect.mArg))
+                            converter->convert(*refNum, refNum->mIndex);
+                    }
+                }
+            };
+            convertSummons(mSpells);
+            convertSummons(mQueue);
+        }
     }
 
     void ActiveSpells::unloadActor(const MWWorld::Ptr& ptr)
diff --git a/apps/openmw/mwmechanics/activespells.hpp b/apps/openmw/mwmechanics/activespells.hpp
index 32046256fd..c465e28556 100644
--- a/apps/openmw/mwmechanics/activespells.hpp
+++ b/apps/openmw/mwmechanics/activespells.hpp
@@ -37,7 +37,7 @@ namespace MWMechanics
             ESM::RefId mSourceSpellId;
             std::vector<ActiveEffect> mEffects;
             std::string mDisplayName;
-            int mCasterActorId;
+            ESM::RefNum mCaster;
             ESM::RefNum mItem;
             ESM::ActiveSpells::Flags mFlags;
             int mWorsenings;
@@ -69,7 +69,7 @@ namespace MWMechanics
             const std::vector<ActiveEffect>& getEffects() const { return mEffects; }
             std::vector<ActiveEffect>& getEffects() { return mEffects; }
 
-            int getCasterActorId() const { return mCasterActorId; }
+            ESM::RefNum getCaster() const { return mCaster; }
 
             int getWorsenings() const { return mWorsenings; }
 
@@ -157,8 +157,8 @@ namespace MWMechanics
         void purge(EffectPredicate predicate, const MWWorld::Ptr& ptr);
         void purge(ParamsPredicate predicate, const MWWorld::Ptr& ptr);
 
-        /// Remove all effects that were cast by \a casterActorId
-        void purge(const MWWorld::Ptr& ptr, int casterActorId);
+        /// Remove all effects that were cast by \a actor
+        void purge(const MWWorld::Ptr& ptr, ESM::RefNum actor);
 
         /// Remove all spells
         void clear(const MWWorld::Ptr& ptr);
diff --git a/apps/openmw/mwmechanics/actors.cpp b/apps/openmw/mwmechanics/actors.cpp
index 786539e585..0f1fe34701 100644
--- a/apps/openmw/mwmechanics/actors.cpp
+++ b/apps/openmw/mwmechanics/actors.cpp
@@ -25,6 +25,7 @@
 #include "../mwworld/inventorystore.hpp"
 #include "../mwworld/player.hpp"
 #include "../mwworld/scene.hpp"
+#include "../mwworld/worldmodel.hpp"
 
 #include "../mwbase/dialoguemanager.hpp"
 #include "../mwbase/environment.hpp"
@@ -178,7 +179,7 @@ namespace
             {
                 if (effect.mEffectId != ESM::MagicEffect::Soultrap || effect.mMagnitude <= 0.f)
                     continue;
-                MWWorld::Ptr caster = world->searchPtrViaActorId(params.getCasterActorId());
+                MWWorld::Ptr caster = MWBase::Environment::get().getWorldModel()->getPtr(params.getCaster());
                 if (caster.isEmpty() || !caster.getClass().isActor())
                     continue;
 
@@ -641,12 +642,13 @@ namespace MWMechanics
             if (creatureStats1.getAiSequence().isInCombat(ally))
                 continue;
 
-            if (creatureStats2.matchesActorId(ally.getClass().getCreatureStats(ally).getHitAttemptActorId()))
+            ESM::RefNum allyHitNum = ally.getClass().getCreatureStats(ally).getHitAttemptActor();
+            if (allyHitNum.isSet() && actor2.getCellRef().getRefNum() == allyHitNum)
             {
                 mechanicsManager->startCombat(actor1, actor2, &cachedAllies.getActorsSidingWith(actor2));
                 // Also set the same hit attempt actor. Otherwise, if fighting the player, they may stop combat
                 // if the player gets out of reach, while the ally would continue combat with the player
-                creatureStats1.setHitAttemptActorId(ally.getClass().getCreatureStats(ally).getHitAttemptActorId());
+                creatureStats1.setHitAttemptActor(allyHitNum);
                 return;
             }
 
@@ -789,8 +791,7 @@ namespace MWMechanics
             {
                 bool actorKilled = false;
 
-                MWWorld::Ptr caster
-                    = MWBase::Environment::get().getWorld()->searchPtrViaActorId(spell.getCasterActorId());
+                MWWorld::Ptr caster = MWBase::Environment::get().getWorldModel()->getPtr(spell.getCaster());
                 if (caster.isEmpty())
                     continue;
                 for (const auto& effect : spell.getEffects())
@@ -831,7 +832,7 @@ namespace MWMechanics
         if (!creature.isInCell())
             return;
 
-        if (!creatureStats.getSummonedCreatureMap().empty() || !creatureStats.getSummonedCreatureGraveyard().empty())
+        if (!creatureStats.getSummonedCreatureMap().empty())
             updateSummons(creature, mTimerDisposeSummonsCorpses == 0.f);
     }
 
@@ -1155,9 +1156,10 @@ namespace MWMechanics
                     = esmStore.get<ESM::GameSetting>().find("iCrimeThresholdMultiplier")->mValue.getInteger();
                 if (playerStats.getBounty() >= cutoff * iCrimeThresholdMultiplier)
                 {
+                    ESM::RefNum playerNum = player.getCellRef().getRefNum();
                     mechanicsManager->startCombat(ptr, player, &cachedAllies.getActorsSidingWith(player));
                     // Stops the guard from quitting combat if player is unreachable
-                    creatureStats.setHitAttemptActorId(playerClass.getCreatureStats(player).getActorId());
+                    creatureStats.setHitAttemptActor(playerNum);
                 }
                 else
                     creatureStats.getAiSequence().stack(AiPursue(player), ptr);
@@ -1517,13 +1519,14 @@ namespace MWMechanics
             SidingCache cachedAllies{ *this, true }; // will be filled as engageCombat iterates
 
             const bool aiActive = MWBase::Environment::get().getMechanicsManager()->isAIActive();
-            const int attackedByPlayerId = player.getClass().getCreatureStats(player).getHitAttemptActorId();
-            if (attackedByPlayerId != -1)
+            const ESM::RefNum attackedByPlayerNum = player.getClass().getCreatureStats(player).getHitAttemptActor();
+            if (attackedByPlayerNum.isSet())
             {
-                const MWWorld::Ptr playerHitAttemptActor = world->searchPtrViaActorId(attackedByPlayerId);
+                const MWWorld::Ptr playerHitAttemptActor
+                    = MWBase::Environment::get().getWorldModel()->getPtr(attackedByPlayerNum);
 
                 if (!playerHitAttemptActor.isInCell())
-                    player.getClass().getCreatureStats(player).setHitAttemptActorId(-1);
+                    player.getClass().getCreatureStats(player).setHitAttemptActor({});
             }
             const int actorsProcessingRange = Settings::game().mActorsProcessingRange;
 
@@ -1548,10 +1551,10 @@ namespace MWMechanics
                         || !actor.getPtr().getClass().getCreatureStats(actor.getPtr()).getAiSequence().isInCombat()
                         || !inProcessingRange))
                 {
-                    actor.getPtr().getClass().getCreatureStats(actor.getPtr()).setHitAttemptActorId(-1);
-                    if (player.getClass().getCreatureStats(player).getHitAttemptActorId()
-                        == actor.getPtr().getClass().getCreatureStats(actor.getPtr()).getActorId())
-                        player.getClass().getCreatureStats(player).setHitAttemptActorId(-1);
+                    actor.getPtr().getClass().getCreatureStats(actor.getPtr()).setHitAttemptActor({});
+                    ESM::RefNum playerHitNum = player.getClass().getCreatureStats(player).getHitAttemptActor();
+                    if (playerHitNum.isSet() && playerHitNum == actor.getPtr().getCellRef().getRefNum())
+                        player.getClass().getCreatureStats(player).setHitAttemptActor({});
                 }
 
                 const Misc::TimerStatus engageCombatTimerStatus = actor.updateEngageCombatTimer(duration);
@@ -1812,7 +1815,7 @@ namespace MWMechanics
                     = stats.getMagicEffects().getOrDefault(ESM::MagicEffect::Vampirism).getMagnitude();
                 stats.getActiveSpells().clear(actor.getPtr());
                 // Make sure spell effects are removed
-                purgeSpellEffects(stats.getActorId());
+                purgeSpellEffects(actor.getPtr().getCellRef().getRefNum());
 
                 stats.getMagicEffects().add(ESM::MagicEffect::Vampirism, vampirism);
 
@@ -1830,9 +1833,9 @@ namespace MWMechanics
         }
     }
 
-    void Actors::cleanupSummonedCreature(MWMechanics::CreatureStats& casterStats, int creatureActorId) const
+    void Actors::cleanupSummonedCreature(ESM::RefNum creature) const
     {
-        const MWWorld::Ptr ptr = MWBase::Environment::get().getWorld()->searchPtrViaActorId(creatureActorId);
+        const MWWorld::Ptr ptr = MWBase::Environment::get().getWorldModel()->getPtr(creature);
         if (!ptr.isEmpty())
         {
             MWBase::Environment::get().getWorld()->deleteObject(ptr);
@@ -1845,24 +1848,16 @@ namespace MWMechanics
                     ptr.getRefData().getPosition().asVec3());
 
             // Remove the summoned creature's summoned creatures as well
-            MWMechanics::CreatureStats& stats = ptr.getClass().getCreatureStats(ptr);
-            auto& creatureMap = stats.getSummonedCreatureMap();
-            for (const auto& creature : creatureMap)
-                cleanupSummonedCreature(stats, creature.second);
+            auto& creatureMap = ptr.getClass().getCreatureStats(ptr).getSummonedCreatureMap();
+            for (const auto& [_, refNum] : creatureMap)
+                cleanupSummonedCreature(refNum);
             creatureMap.clear();
         }
-        else if (creatureActorId != -1)
-        {
-            // We didn't find the creature. It's probably in an inactive cell.
-            // Add to graveyard so we can delete it when the cell becomes active.
-            std::vector<int>& graveyard = casterStats.getSummonedCreatureGraveyard();
-            graveyard.push_back(creatureActorId);
-        }
 
-        purgeSpellEffects(creatureActorId);
+        purgeSpellEffects(creature);
     }
 
-    void Actors::purgeSpellEffects(int casterActorId) const
+    void Actors::purgeSpellEffects(ESM::RefNum creature) const
     {
         for (const Actor& actor : mActors)
         {
@@ -1870,7 +1865,7 @@ namespace MWMechanics
                 continue;
             MWMechanics::ActiveSpells& spells
                 = actor.getPtr().getClass().getCreatureStats(actor.getPtr()).getActiveSpells();
-            spells.purge(actor.getPtr(), casterActorId);
+            spells.purge(actor.getPtr(), creature);
         }
     }
 
diff --git a/apps/openmw/mwmechanics/actors.hpp b/apps/openmw/mwmechanics/actors.hpp
index 3e34ed0d67..a941aa0395 100644
--- a/apps/openmw/mwmechanics/actors.hpp
+++ b/apps/openmw/mwmechanics/actors.hpp
@@ -35,7 +35,6 @@ namespace MWMechanics
 {
     class Actor;
     class CharacterController;
-    class CreatureStats;
     class SidingCache;
 
     class Actors
@@ -128,7 +127,7 @@ namespace MWMechanics
 
         bool isAnyObjectInRange(const osg::Vec3f& position, float radius) const;
 
-        void cleanupSummonedCreature(CreatureStats& casterStats, int creatureActorId) const;
+        void cleanupSummonedCreature(ESM::RefNum creature) const;
 
         /// Returns the list of actors which are siding with the given actor in fights
         /**ie AiFollow or AiEscort is active and the target is the actor **/
@@ -189,7 +188,7 @@ namespace MWMechanics
 
         void killDeadActors();
 
-        void purgeSpellEffects(int casterActorId) const;
+        void purgeSpellEffects(ESM::RefNum creature) const;
 
         void predictAndAvoidCollisions(float duration) const;
 
diff --git a/apps/openmw/mwmechanics/aicombat.cpp b/apps/openmw/mwmechanics/aicombat.cpp
index 0ddcf409b6..2b71f2e8a5 100644
--- a/apps/openmw/mwmechanics/aicombat.cpp
+++ b/apps/openmw/mwmechanics/aicombat.cpp
@@ -36,18 +36,24 @@ namespace
 
     osg::Vec3f AimDirToMovingTarget(const MWWorld::Ptr& actor, const MWWorld::Ptr& target,
         const osg::Vec3f& vLastTargetPos, float duration, int weapType, float strength);
+
+    bool hitAttemptMatchesTarget(const MWWorld::Ptr& actor, const MWWorld::Ptr& target)
+    {
+        ESM::RefNum hitNum = actor.getClass().getCreatureStats(actor).getHitAttemptActor();
+        return hitNum.isSet() && target.getCellRef().getRefNum() == hitNum;
+    }
 }
 
 namespace MWMechanics
 {
     AiCombat::AiCombat(const MWWorld::Ptr& actor)
     {
-        mTargetActorId = actor.getClass().getCreatureStats(actor).getActorId();
+        mTargetActor = actor.getCellRef().getRefNum();
     }
 
     AiCombat::AiCombat(const ESM::AiSequence::AiCombat* combat)
     {
-        mTargetActorId = combat->mTargetActorId;
+        mTargetActor = combat->mTargetActor;
     }
 
     void AiCombat::init() {}
@@ -109,14 +115,11 @@ namespace MWMechanics
         if (actor.getClass().getCreatureStats(actor).isDead())
             return true;
 
-        MWWorld::Ptr target = MWBase::Environment::get().getWorld()->searchPtrViaActorId(mTargetActorId);
-        if (target.isEmpty())
-            return true;
+        const MWWorld::Ptr target = getTarget(); // The target to follow
 
-        if (!target.getCellRef().getCount()
-            || !target.getRefData().isEnabled() // Really we should be checking whether the target is currently
-                                                // registered with the MechanicsManager
-            || target.getClass().getCreatureStats(target).isDead())
+        // Stop if the target doesn't exist
+        if (target.isEmpty() || !target.getCellRef().getCount() || !target.getRefData().isEnabled()
+            || target.getClass().getCreatureStats(target).isDead() || !target.getRefData().getBaseNode())
             return true;
 
         if (actor == target) // This should never happen.
@@ -194,8 +197,7 @@ namespace MWMechanics
                 = (std::find(playerFollowersAndEscorters.begin(), playerFollowersAndEscorters.end(), target)
                     != playerFollowersAndEscorters.end());
             if ((target == MWMechanics::getPlayer() || targetSidesWithPlayer)
-                && ((stats.getHitAttemptActorId() == target.getClass().getCreatureStats(target).getActorId())
-                    || (target.getClass().getCreatureStats(target).getHitAttemptActorId() == stats.getActorId())))
+                && (hitAttemptMatchesTarget(actor, target) || hitAttemptMatchesTarget(target, actor)))
                 forceFlee = true;
             else // Otherwise end combat
                 return true;
@@ -491,19 +493,10 @@ namespace MWMechanics
         storage.mRotateMove = !smoothTurn(actor, targetAngleRadians, axis, eps);
     }
 
-    MWWorld::Ptr AiCombat::getTarget() const
-    {
-        if (mCachedTarget.isEmpty() || mCachedTarget.mRef->isDeleted() || !mCachedTarget.getRefData().isEnabled())
-        {
-            mCachedTarget = MWBase::Environment::get().getWorld()->searchPtrViaActorId(mTargetActorId);
-        }
-        return mCachedTarget;
-    }
-
     void AiCombat::writeState(ESM::AiSequence::AiSequence& sequence) const
     {
         auto combat = std::make_unique<ESM::AiSequence::AiCombat>();
-        combat->mTargetActorId = mTargetActorId;
+        combat->mTargetActor = mTargetActor;
 
         ESM::AiSequence::AiPackageContainer package;
         package.mType = ESM::AiSequence::Ai_Combat;
diff --git a/apps/openmw/mwmechanics/aicombat.hpp b/apps/openmw/mwmechanics/aicombat.hpp
index 42baaf6349..4102a6218a 100644
--- a/apps/openmw/mwmechanics/aicombat.hpp
+++ b/apps/openmw/mwmechanics/aicombat.hpp
@@ -100,9 +100,6 @@ namespace MWMechanics
             return options;
         }
 
-        /// Returns target ID
-        MWWorld::Ptr getTarget() const override;
-
         void writeState(ESM::AiSequence::AiSequence& sequence) const override;
 
     private:
diff --git a/apps/openmw/mwmechanics/aiescort.cpp b/apps/openmw/mwmechanics/aiescort.cpp
index a375aea33c..553e41bec6 100644
--- a/apps/openmw/mwmechanics/aiescort.cpp
+++ b/apps/openmw/mwmechanics/aiescort.cpp
@@ -24,15 +24,16 @@
 
 namespace MWMechanics
 {
-    AiEscort::AiEscort(const ESM::RefId& actorId, int duration, float x, float y, float z, bool repeat)
+    AiEscort::AiEscort(ESM::RefNum actor, std::string_view cellId, int duration, float x, float y, float z, bool repeat)
         : TypedAiPackage<AiEscort>(repeat)
+        , mCellId(cellId)
         , mX(x)
         , mY(y)
         , mZ(z)
         , mDuration(static_cast<float>(duration))
         , mRemainingDuration(static_cast<float>(duration))
     {
-        mTargetActorRefId = actorId;
+        mTargetActor = actor;
     }
 
     AiEscort::AiEscort(
@@ -58,7 +59,7 @@ namespace MWMechanics
         , mRemainingDuration(escort->mRemainingDuration)
     {
         mTargetActorRefId = escort->mTargetId;
-        mTargetActorId = escort->mTargetActorId;
+        mTargetActor = escort->mTargetActor;
     }
 
     bool AiEscort::execute(
@@ -131,7 +132,7 @@ namespace MWMechanics
         escort->mData.mZ = mZ;
         escort->mData.mDuration = static_cast<int16_t>(mDuration);
         escort->mTargetId = mTargetActorRefId;
-        escort->mTargetActorId = mTargetActorId;
+        escort->mTargetActor = mTargetActor;
         escort->mRemainingDuration = mRemainingDuration;
         escort->mCellId = mCellId;
         escort->mRepeat = getRepeat();
diff --git a/apps/openmw/mwmechanics/aiescort.hpp b/apps/openmw/mwmechanics/aiescort.hpp
index d88ecac6a5..e37196e134 100644
--- a/apps/openmw/mwmechanics/aiescort.hpp
+++ b/apps/openmw/mwmechanics/aiescort.hpp
@@ -20,13 +20,10 @@ namespace MWMechanics
     class AiEscort final : public TypedAiPackage<AiEscort>
     {
     public:
-        /// Implementation of AiEscort
-        /** The Actor will escort the specified actor to the world position x, y, z until they reach their position, or
+        /** The Actor will escort the specified actor to the position x, y, z until they reach their position, or
            they run out of time \implement AiEscort **/
-        AiEscort(const ESM::RefId& actorId, int duration, float x, float y, float z, bool repeat);
-        /// Implementation of AiEscortCell
-        /** The Actor will escort the specified actor to the cell position x, y, z until they reach their position, or
-           they run out of time \implement AiEscortCell **/
+        AiEscort(ESM::RefNum actor, std::string_view cellId, int duration, float x, float y, float z, bool repeat);
+        /// Implementation of AiEscort/AiEscortCell
         AiEscort(
             const ESM::RefId& actorId, std::string_view cellId, int duration, float x, float y, float z, bool repeat);
 
diff --git a/apps/openmw/mwmechanics/aifollow.cpp b/apps/openmw/mwmechanics/aifollow.cpp
index ec128ae2a9..7f2f3a0fef 100644
--- a/apps/openmw/mwmechanics/aifollow.cpp
+++ b/apps/openmw/mwmechanics/aifollow.cpp
@@ -30,7 +30,8 @@ namespace MWMechanics
 {
     int AiFollow::mFollowIndexCounter = 0;
 
-    AiFollow::AiFollow(const ESM::RefId& actorId, float duration, float x, float y, float z, bool repeat)
+    AiFollow::AiFollow(
+        ESM::RefNum actor, std::string_view cellId, float duration, float x, float y, float z, bool repeat)
         : TypedAiPackage<AiFollow>(repeat)
         , mAlwaysFollow(false)
         , mDuration(duration)
@@ -38,10 +39,11 @@ namespace MWMechanics
         , mX(x)
         , mY(y)
         , mZ(z)
+        , mCellId(cellId)
         , mActive(false)
         , mFollowIndex(mFollowIndexCounter++)
     {
-        mTargetActorRefId = actorId;
+        mTargetActor = actor;
     }
 
     AiFollow::AiFollow(
@@ -72,7 +74,7 @@ namespace MWMechanics
         , mFollowIndex(mFollowIndexCounter++)
     {
         mTargetActorRefId = actor.getCellRef().getRefId();
-        mTargetActorId = actor.getClass().getCreatureStats(actor).getActorId();
+        mTargetActor = actor.getCellRef().getRefNum();
     }
 
     AiFollow::AiFollow(const ESM::AiSequence::AiFollow* follow)
@@ -89,7 +91,7 @@ namespace MWMechanics
         , mFollowIndex(mFollowIndexCounter++)
     {
         mTargetActorRefId = follow->mTargetId;
-        mTargetActorId = follow->mTargetActorId;
+        mTargetActor = follow->mTargetActor;
     }
 
     bool AiFollow::execute(
@@ -246,7 +248,7 @@ namespace MWMechanics
         follow->mData.mZ = mZ;
         follow->mData.mDuration = static_cast<int16_t>(mDuration);
         follow->mTargetId = mTargetActorRefId;
-        follow->mTargetActorId = mTargetActorId;
+        follow->mTargetActor = mTargetActor;
         follow->mRemainingDuration = mRemainingDuration;
         follow->mCellId = mCellId;
         follow->mAlwaysFollow = mAlwaysFollow;
diff --git a/apps/openmw/mwmechanics/aifollow.hpp b/apps/openmw/mwmechanics/aifollow.hpp
index 85d11977ca..94c8a35efc 100644
--- a/apps/openmw/mwmechanics/aifollow.hpp
+++ b/apps/openmw/mwmechanics/aifollow.hpp
@@ -41,9 +41,7 @@ namespace MWMechanics
     class AiFollow final : public TypedAiPackage<AiFollow>
     {
     public:
-        /// Follow Actor for duration or until you arrive at a world position
-        AiFollow(const ESM::RefId& actorId, float duration, float x, float y, float z, bool repeat);
-        /// Follow Actor for duration or until you arrive at a position in a cell
+        AiFollow(ESM::RefNum actor, std::string_view cellId, float duration, float x, float y, float z, bool repeat);
         AiFollow(
             const ESM::RefId& actorId, std::string_view cellId, float duration, float x, float y, float z, bool repeat);
         /// Follow Actor indefinitely
diff --git a/apps/openmw/mwmechanics/aipackage.cpp b/apps/openmw/mwmechanics/aipackage.cpp
index 146124fcbf..d7daae0e98 100644
--- a/apps/openmw/mwmechanics/aipackage.cpp
+++ b/apps/openmw/mwmechanics/aipackage.cpp
@@ -16,6 +16,7 @@
 #include "../mwworld/class.hpp"
 #include "../mwworld/containerstore.hpp"
 #include "../mwworld/esmstore.hpp"
+#include "../mwworld/worldmodel.hpp"
 
 #include "../mwphysics/raycasting.hpp"
 
@@ -51,71 +52,35 @@ MWMechanics::AiPackage::AiPackage(AiPackageTypeId typeId, const Options& options
     : mTypeId(typeId)
     , mOptions(options)
     , mReaction(MWBase::Environment::get().getWorld()->getPrng())
-    , mTargetActorId(-1)
-    , mCachedTarget()
-    , mRotateOnTheRunChecks(0)
-    , mIsShortcutting(false)
-    , mShortcutProhibited(false)
-    , mShortcutFailPos()
 {
 }
 
 MWWorld::Ptr MWMechanics::AiPackage::getTarget() const
 {
-    if (!mCachedTarget.isEmpty())
-    {
-        if (mCachedTarget.mRef->isDeleted() || !mCachedTarget.getRefData().isEnabled())
-            mCachedTarget = MWWorld::Ptr();
-        else
-            return mCachedTarget;
-    }
-
-    if (mTargetActorId == -2)
-        return MWWorld::Ptr();
-
-    if (mTargetActorId == -1)
-    {
-        if (mTargetActorRefId.empty())
-        {
-            mTargetActorId = -2;
-            return MWWorld::Ptr();
-        }
-        mCachedTarget = MWBase::Environment::get().getWorld()->searchPtr(mTargetActorRefId, false);
-        if (mCachedTarget.isEmpty())
-        {
-            mTargetActorId = -2;
-            return mCachedTarget;
-        }
-        else
-            mTargetActorId = mCachedTarget.getClass().getCreatureStats(mCachedTarget).getActorId();
-    }
-
-    if (mTargetActorId != -1)
-        mCachedTarget = MWBase::Environment::get().getWorld()->searchPtrViaActorId(mTargetActorId);
+    if (mTargetActor.isSet())
+        return MWBase::Environment::get().getWorldModel()->getPtr(mTargetActor);
+    if (mTargetActorRefId.empty() || mTargetNotFound)
+        return {};
+    MWWorld::Ptr ptr = MWBase::Environment::get().getWorld()->searchPtr(mTargetActorRefId, false);
+    if (ptr.isEmpty())
+        mTargetNotFound = true;
     else
-        return MWWorld::Ptr();
-
-    return mCachedTarget;
+    {
+        MWBase::Environment::get().getWorldModel()->registerPtr(ptr);
+        mTargetActor = ptr.getCellRef().getRefNum();
+    }
+    return ptr;
 }
 
 bool MWMechanics::AiPackage::targetIs(const MWWorld::Ptr& ptr) const
 {
-    if (mTargetActorId == -2)
-        return ptr.isEmpty();
-    else if (mTargetActorId == -1)
-    {
-        if (mTargetActorRefId.empty())
-        {
-            mTargetActorId = -2;
-            return ptr.isEmpty();
-        }
-        if (!ptr.isEmpty() && ptr.getCellRef().getRefId() == mTargetActorRefId)
-            return getTarget() == ptr;
+    if (ptr.isEmpty())
+        return getTarget() == ptr;
+    if (mTargetActor.isSet())
+        return ptr.getCellRef().getRefNum() == mTargetActor;
+    if (ptr.getCellRef().getRefId() != mTargetActorRefId)
         return false;
-    }
-    if (ptr.isEmpty() || !ptr.getClass().isActor())
-        return false;
-    return ptr.getClass().getCreatureStats(ptr).getActorId() == mTargetActorId;
+    return getTarget() == ptr;
 }
 
 void MWMechanics::AiPackage::reset()
@@ -125,7 +90,7 @@ void MWMechanics::AiPackage::reset()
     mIsShortcutting = false;
     mShortcutProhibited = false;
     mShortcutFailPos = osg::Vec3f();
-    mCachedTarget = MWWorld::Ptr();
+    mTargetNotFound = false;
 
     mPathFinder.clearPath();
     mObstacleCheck.clear();
diff --git a/apps/openmw/mwmechanics/aipackage.hpp b/apps/openmw/mwmechanics/aipackage.hpp
index 42aa62ffe3..fbae265cc6 100644
--- a/apps/openmw/mwmechanics/aipackage.hpp
+++ b/apps/openmw/mwmechanics/aipackage.hpp
@@ -26,6 +26,7 @@ namespace ESM
 
 namespace MWMechanics
 {
+    class AiSequence;
     class CharacterController;
     class PathgridGraph;
 
@@ -171,15 +172,15 @@ namespace MWMechanics
         AiReactionTimer mReaction;
 
         ESM::RefId mTargetActorRefId;
-        mutable int mTargetActorId;
-        mutable MWWorld::Ptr mCachedTarget;
-
-        short mRotateOnTheRunChecks; // attempts to check rotation to the pathpoint on the run possibility
-
-        bool mIsShortcutting; // if shortcutting at the moment
-        bool mShortcutProhibited; // shortcutting may be prohibited after unsuccessful attempt
+        mutable ESM::RefNum mTargetActor;
         osg::Vec3f mShortcutFailPos; // position of last shortcut fail
         float mLastDestinationTolerance = 0;
+        short mRotateOnTheRunChecks = 0; // attempts to check rotation to the pathpoint on the run possibility
+        mutable bool mTargetNotFound = false;
+        bool mIsShortcutting = false; // if shortcutting at the moment
+        bool mShortcutProhibited = false; // shortcutting may be prohibited after unsuccessful attempt
+
+        friend class AiSequence;
 
     private:
         bool isNearInactiveCell(osg::Vec3f position);
diff --git a/apps/openmw/mwmechanics/aipursue.cpp b/apps/openmw/mwmechanics/aipursue.cpp
index 1dbbddd218..b9bc3d9966 100644
--- a/apps/openmw/mwmechanics/aipursue.cpp
+++ b/apps/openmw/mwmechanics/aipursue.cpp
@@ -19,12 +19,12 @@ namespace MWMechanics
 
     AiPursue::AiPursue(const MWWorld::Ptr& actor)
     {
-        mTargetActorId = actor.getClass().getCreatureStats(actor).getActorId();
+        mTargetActor = actor.getCellRef().getRefNum();
     }
 
     AiPursue::AiPursue(const ESM::AiSequence::AiPursue* pursue)
     {
-        mTargetActorId = pursue->mTargetActorId;
+        mTargetActor = pursue->mTargetActor;
     }
 
     bool AiPursue::execute(
@@ -33,12 +33,11 @@ namespace MWMechanics
         if (actor.getClass().getCreatureStats(actor).isDead())
             return true;
 
-        const MWWorld::Ptr target
-            = MWBase::Environment::get().getWorld()->searchPtrViaActorId(mTargetActorId); // The target to follow
+        const MWWorld::Ptr target = getTarget(); // The target to follow
 
         // Stop if the target doesn't exist
-        // Really we should be checking whether the target is currently registered with the MechanicsManager
-        if (target == MWWorld::Ptr() || !target.getCellRef().getCount() || !target.getRefData().isEnabled())
+        if (target.isEmpty() || !target.getCellRef().getCount() || !target.getRefData().isEnabled()
+            || !target.getRefData().getBaseNode())
             return true;
 
         if (isTargetMagicallyHidden(target)
@@ -79,23 +78,10 @@ namespace MWMechanics
         return false;
     }
 
-    MWWorld::Ptr AiPursue::getTarget() const
-    {
-        if (!mCachedTarget.isEmpty())
-        {
-            if (mCachedTarget.mRef->isDeleted() || !mCachedTarget.getRefData().isEnabled())
-                mCachedTarget = MWWorld::Ptr();
-            else
-                return mCachedTarget;
-        }
-        mCachedTarget = MWBase::Environment::get().getWorld()->searchPtrViaActorId(mTargetActorId);
-        return mCachedTarget;
-    }
-
     void AiPursue::writeState(ESM::AiSequence::AiSequence& sequence) const
     {
         auto pursue = std::make_unique<ESM::AiSequence::AiPursue>();
-        pursue->mTargetActorId = mTargetActorId;
+        pursue->mTargetActor = mTargetActor;
 
         ESM::AiSequence::AiPackageContainer package;
         package.mType = ESM::AiSequence::Ai_Pursue;
diff --git a/apps/openmw/mwmechanics/aipursue.hpp b/apps/openmw/mwmechanics/aipursue.hpp
index d9cf4a40c3..c7ed7e04f5 100644
--- a/apps/openmw/mwmechanics/aipursue.hpp
+++ b/apps/openmw/mwmechanics/aipursue.hpp
@@ -39,8 +39,6 @@ namespace MWMechanics
             return options;
         }
 
-        MWWorld::Ptr getTarget() const override;
-
         void writeState(ESM::AiSequence::AiSequence& sequence) const override;
     };
 }
diff --git a/apps/openmw/mwmechanics/aisequence.cpp b/apps/openmw/mwmechanics/aisequence.cpp
index 70b94b1eba..a532f55c1a 100644
--- a/apps/openmw/mwmechanics/aisequence.cpp
+++ b/apps/openmw/mwmechanics/aisequence.cpp
@@ -4,6 +4,7 @@
 #include <limits>
 
 #include <components/debug/debuglog.hpp>
+#include <components/esm3/actoridconverter.hpp>
 #include <components/esm3/aisequence.hpp>
 
 #include "../mwbase/environment.hpp"
@@ -538,6 +539,7 @@ namespace MWMechanics
         for (auto& container : sequence.mPackages)
         {
             std::unique_ptr<MWMechanics::AiPackage> package;
+            bool hasTarget = false;
             switch (container.mType)
             {
                 case ESM::AiSequence::Ai_Wander:
@@ -560,12 +562,14 @@ namespace MWMechanics
                 {
                     package = std::make_unique<AiEscort>(
                         &static_cast<const ESM::AiSequence::AiEscort&>(*container.mPackage));
+                    hasTarget = true;
                     break;
                 }
                 case ESM::AiSequence::Ai_Follow:
                 {
                     package = std::make_unique<AiFollow>(
                         &static_cast<const ESM::AiSequence::AiFollow&>(*container.mPackage));
+                    hasTarget = true;
                     break;
                 }
                 case ESM::AiSequence::Ai_Activate:
@@ -578,12 +582,14 @@ namespace MWMechanics
                 {
                     package = std::make_unique<AiCombat>(
                         &static_cast<const ESM::AiSequence::AiCombat&>(*container.mPackage));
+                    hasTarget = true;
                     break;
                 }
                 case ESM::AiSequence::Ai_Pursue:
                 {
                     package = std::make_unique<AiPursue>(
                         &static_cast<const ESM::AiSequence::AiPursue&>(*container.mPackage));
+                    hasTarget = true;
                     break;
                 }
                 default:
@@ -592,6 +598,8 @@ namespace MWMechanics
 
             if (!package.get())
                 continue;
+            if (hasTarget && sequence.mActorIdConverter)
+                sequence.mActorIdConverter->convert(package->mTargetActor, package->mTargetActor.mIndex);
 
             onPackageAdded(*package);
             mPackages.push_back(std::move(package));
diff --git a/apps/openmw/mwmechanics/creaturestats.cpp b/apps/openmw/mwmechanics/creaturestats.cpp
index 24b5891c1c..e52abefed6 100644
--- a/apps/openmw/mwmechanics/creaturestats.cpp
+++ b/apps/openmw/mwmechanics/creaturestats.cpp
@@ -3,6 +3,7 @@
 #include <algorithm>
 #include <type_traits>
 
+#include <components/esm3/actoridconverter.hpp>
 #include <components/esm3/creaturestats.hpp>
 #include <components/esm3/esmreader.hpp>
 #include <components/esm3/esmwriter.hpp>
@@ -17,8 +18,6 @@
 
 namespace MWMechanics
 {
-    int CreatureStats::sActorId = 0;
-
     CreatureStats::CreatureStats()
     {
         for (const ESM::Attribute& attribute : MWBase::Environment::get().getESMStore()->get<ESM::Attribute>())
@@ -365,14 +364,14 @@ namespace MWMechanics
         return mLastHitAttemptObject;
     }
 
-    void CreatureStats::setHitAttemptActorId(int actorId)
+    void CreatureStats::setHitAttemptActor(ESM::RefNum actor)
     {
-        mHitAttemptActorId = actorId;
+        mHitAttemptActor = actor;
     }
 
-    int CreatureStats::getHitAttemptActorId() const
+    ESM::RefNum CreatureStats::getHitAttemptActor() const
     {
-        return mHitAttemptActorId;
+        return mHitAttemptActor;
     }
 
     void CreatureStats::addToFallHeight(float height)
@@ -539,7 +538,6 @@ namespace MWMechanics
         state.mRecalcDynamicStats = false;
         state.mDrawState = static_cast<int>(mDrawState);
         state.mLevel = mLevel;
-        state.mActorId = mActorId;
         state.mDeathAnimation = mDeathAnimation;
         state.mTimeOfDeath = mTimeOfDeath.toEsm();
         // state.mHitAttemptActorId = mHitAttemptActorId;
@@ -550,7 +548,6 @@ namespace MWMechanics
         mMagicEffects.writeState(state.mMagicEffects);
 
         state.mSummonedCreatures = mSummonedCreatures;
-        state.mSummonGraveyard = mSummonGraveyard;
 
         state.mHasAiSettings = true;
         for (size_t i = 0; i < state.mAiSettings.size(); ++i)
@@ -593,10 +590,9 @@ namespace MWMechanics
         mLastHitAttemptObject = state.mLastHitAttemptObject;
         mDrawState = DrawState(state.mDrawState);
         mLevel = state.mLevel;
-        mActorId = state.mActorId;
         mDeathAnimation = state.mDeathAnimation;
         mTimeOfDeath = MWWorld::TimeStamp(state.mTimeOfDeath);
-        // mHitAttemptActorId = state.mHitAttemptActorId;
+        // mHitAttemptActor = state.mHitAttemptActor;
 
         mSpells.readState(state.mSpells, this);
         mActiveSpells.readState(state.mActiveSpells);
@@ -604,13 +600,19 @@ namespace MWMechanics
         mMagicEffects.readState(state.mMagicEffects);
 
         mSummonedCreatures = state.mSummonedCreatures;
-        mSummonGraveyard = state.mSummonGraveyard;
 
         if (state.mHasAiSettings)
             for (size_t i = 0; i < state.mAiSettings.size(); ++i)
                 mAiSettings[i].readState(state.mAiSettings[i]);
         if (state.mRecalcDynamicStats)
             recalculateMagicka();
+        if (state.mAiSequence.mActorIdConverter)
+        {
+            for (auto& [_, refNum] : mSummonedCreatures)
+                state.mAiSequence.mActorIdConverter->convert(refNum, refNum.mIndex);
+            auto& graveyard = state.mAiSequence.mActorIdConverter->mGraveyard;
+            graveyard.insert(graveyard.end(), state.mSummonGraveyard.begin(), state.mSummonGraveyard.end());
+        }
     }
 
     void CreatureStats::setLastRestockTime(MWWorld::TimeStamp tradeTime)
@@ -632,36 +634,6 @@ namespace MWMechanics
         return mGoldPool;
     }
 
-    int CreatureStats::getActorId()
-    {
-        if (mActorId == -1)
-            mActorId = sActorId++;
-
-        return mActorId;
-    }
-
-    bool CreatureStats::matchesActorId(int id) const
-    {
-        return mActorId != -1 && id == mActorId;
-    }
-
-    void CreatureStats::cleanup()
-    {
-        sActorId = 0;
-    }
-
-    void CreatureStats::writeActorIdCounter(ESM::ESMWriter& esm)
-    {
-        esm.startRecord(ESM::REC_ACTC);
-        esm.writeHNT("COUN", sActorId);
-        esm.endRecord(ESM::REC_ACTC);
-    }
-
-    void CreatureStats::readActorIdCounter(ESM::ESMReader& esm)
-    {
-        esm.getHNT(sActorId, "COUN");
-    }
-
     signed char CreatureStats::getDeathAnimation() const
     {
         return mDeathAnimation;
@@ -677,16 +649,11 @@ namespace MWMechanics
         return mTimeOfDeath;
     }
 
-    std::multimap<int, int>& CreatureStats::getSummonedCreatureMap()
+    std::multimap<int, ESM::RefNum>& CreatureStats::getSummonedCreatureMap()
     {
         return mSummonedCreatures;
     }
 
-    std::vector<int>& CreatureStats::getSummonedCreatureGraveyard()
-    {
-        return mSummonGraveyard;
-    }
-
     void CreatureStats::updateAwareness(float duration)
     {
         mAwarenessTimer += duration;
diff --git a/apps/openmw/mwmechanics/creaturestats.hpp b/apps/openmw/mwmechanics/creaturestats.hpp
index aa46e9504f..5441fdc28f 100644
--- a/apps/openmw/mwmechanics/creaturestats.hpp
+++ b/apps/openmw/mwmechanics/creaturestats.hpp
@@ -38,7 +38,6 @@ namespace MWMechanics
     ///
     class CreatureStats
     {
-        static int sActorId;
         std::map<ESM::RefId, AttributeValue> mAttributes;
         DynamicStat<float> mDynamic[3]; // health, magicka, fatigue
         DrawState mDrawState = DrawState::Nothing;
@@ -73,10 +72,9 @@ namespace MWMechanics
         // The pool of merchant gold (not in inventory)
         int mGoldPool = 0;
 
-        int mActorId = -1;
         // Stores an actor that attacked this actor. Only one is stored at a time, and it is not changed if a different
         // actor attacks. It is cleared when combat ends.
-        int mHitAttemptActorId = -1;
+        ESM::RefNum mHitAttemptActor;
 
         // The difference between view direction and lower body direction.
         float mSideMovementAngle = 0;
@@ -84,11 +82,7 @@ namespace MWMechanics
         MWWorld::TimeStamp mTimeOfDeath;
 
     private:
-        std::multimap<int, int> mSummonedCreatures; // <Effect, ActorId>
-
-        // Contains ActorIds of summoned creatures with an expired lifetime that have not been deleted yet.
-        // This may be necessary when the creature is in an inactive cell.
-        std::vector<int> mSummonGraveyard;
+        std::multimap<int, ESM::RefNum> mSummonedCreatures; // <Effect, Actor>
 
         float mAwarenessTimer = 0.f;
         int mAwarenessRoll = -1;
@@ -237,8 +231,7 @@ namespace MWMechanics
         void setBlock(bool value);
         bool getBlock() const;
 
-        std::multimap<int, int>& getSummonedCreatureMap(); // <Effect, ActorId of summoned creature>
-        std::vector<int>& getSummonedCreatureGraveyard(); // ActorIds
+        std::multimap<int, ESM::RefNum>& getSummonedCreatureMap(); // <Effect, summoned creature>
 
         enum Flag
         {
@@ -266,16 +259,13 @@ namespace MWMechanics
         void setLastHitAttemptObject(const ESM::RefId& objectid);
         void clearLastHitAttemptObject();
         const ESM::RefId& getLastHitAttemptObject() const;
-        void setHitAttemptActorId(const int actorId);
-        int getHitAttemptActorId() const;
+        void setHitAttemptActor(ESM::RefNum actorId);
+        ESM::RefNum getHitAttemptActor() const;
 
         void writeState(ESM::CreatureStats& state) const;
 
         void readState(const ESM::CreatureStats& state);
 
-        static void writeActorIdCounter(ESM::ESMWriter& esm);
-        static void readActorIdCounter(ESM::ESMReader& esm);
-
         void setLastRestockTime(MWWorld::TimeStamp tradeTime);
         MWWorld::TimeStamp getLastRestockTime() const;
 
@@ -287,15 +277,6 @@ namespace MWMechanics
 
         MWWorld::TimeStamp getTimeOfDeath() const;
 
-        int getActorId();
-        ///< Will generate an actor ID, if the actor does not have one yet.
-
-        bool matchesActorId(int id) const;
-        ///< Check if \a id matches the actor ID of *this (if the actor does not have an ID
-        /// assigned this function will return false).
-
-        static void cleanup();
-
         float getSideMovementAngle() const { return mSideMovementAngle; }
         void setSideMovementAngle(float angle) { mSideMovementAngle = angle; }
 
diff --git a/apps/openmw/mwmechanics/mechanicsmanagerimp.cpp b/apps/openmw/mwmechanics/mechanicsmanagerimp.cpp
index a494153543..856f5ffcf9 100644
--- a/apps/openmw/mwmechanics/mechanicsmanagerimp.cpp
+++ b/apps/openmw/mwmechanics/mechanicsmanagerimp.cpp
@@ -1454,7 +1454,7 @@ namespace MWMechanics
                     }
 
                     startCombat(actor, player, &playerFollowers);
-                    observerStats.setHitAttemptActorId(player.getClass().getCreatureStats(player).getActorId());
+                    observerStats.setHitAttemptActor(player.getCellRef().getRefNum());
 
                     // Apply aggression value to the base Fight rating, so that the actor can continue fighting
                     // after a Calm spell wears off
@@ -1734,8 +1734,9 @@ namespace MWMechanics
             // if guard starts combat with player, guards pursuing player should do the same
             if (ptr.getClass().isClass(ptr, "Guard"))
             {
+                const ESM::RefNum playerNum = target.getCellRef().getRefNum();
                 // Stops guard from ending combat if player is unreachable
-                stats.setHitAttemptActorId(target.getClass().getCreatureStats(target).getActorId());
+                stats.setHitAttemptActor(playerNum);
                 for (const Actor& actor : mActors)
                 {
                     if (actor.isInvalid())
@@ -1749,10 +1750,7 @@ namespace MWMechanics
                             aiSeq.stopPursuit();
                             aiSeq.stack(MWMechanics::AiCombat(target), ptr);
                             // Stops guard from ending combat if player is unreachable
-                            actor.getPtr()
-                                .getClass()
-                                .getCreatureStats(actor.getPtr())
-                                .setHitAttemptActorId(target.getClass().getCreatureStats(target).getActorId());
+                            actor.getPtr().getClass().getCreatureStats(actor.getPtr()).setHitAttemptActor(playerNum);
                         }
                     }
                 }
@@ -2041,9 +2039,9 @@ namespace MWMechanics
         skill.setModifier(acrobatics->mWerewolfValue - skill.getModified());
     }
 
-    void MechanicsManager::cleanupSummonedCreature(const MWWorld::Ptr& caster, int creatureActorId)
+    void MechanicsManager::cleanupSummonedCreature(ESM::RefNum creature)
     {
-        mActors.cleanupSummonedCreature(caster.getClass().getCreatureStats(caster), creatureActorId);
+        mActors.cleanupSummonedCreature(creature);
     }
 
     void MechanicsManager::reportStats(unsigned int frameNumber, osg::Stats& stats) const
diff --git a/apps/openmw/mwmechanics/mechanicsmanagerimp.hpp b/apps/openmw/mwmechanics/mechanicsmanagerimp.hpp
index 53eee5ed83..83da60d99c 100644
--- a/apps/openmw/mwmechanics/mechanicsmanagerimp.hpp
+++ b/apps/openmw/mwmechanics/mechanicsmanagerimp.hpp
@@ -227,7 +227,7 @@ namespace MWMechanics
         void setWerewolf(const MWWorld::Ptr& actor, bool werewolf) override;
         void applyWerewolfAcrobatics(const MWWorld::Ptr& actor) override;
 
-        void cleanupSummonedCreature(const MWWorld::Ptr& caster, int creatureActorId) override;
+        void cleanupSummonedCreature(ESM::RefNum creature) override;
 
         void confiscateStolenItemToOwner(
             const MWWorld::Ptr& player, const MWWorld::Ptr& item, const MWWorld::Ptr& victim, int count) override;
diff --git a/apps/openmw/mwmechanics/spelleffects.cpp b/apps/openmw/mwmechanics/spelleffects.cpp
index a1beca14bb..13a84ba4a0 100644
--- a/apps/openmw/mwmechanics/spelleffects.cpp
+++ b/apps/openmw/mwmechanics/spelleffects.cpp
@@ -33,6 +33,7 @@
 #include "../mwworld/esmstore.hpp"
 #include "../mwworld/inventorystore.hpp"
 #include "../mwworld/player.hpp"
+#include "../mwworld/worldmodel.hpp"
 
 namespace
 {
@@ -1106,6 +1107,7 @@ namespace MWMechanics
         const MWWorld::Ptr& target, ActiveSpells::ActiveSpellParams& spellParams, const ESM::ActiveEffect& effect)
     {
         const auto world = MWBase::Environment::get().getWorld();
+        const auto worldModel = MWBase::Environment::get().getWorldModel();
         auto& magnitudes = target.getClass().getCreatureStats(target).getMagicEffects();
         switch (effect.mEffectId)
         {
@@ -1192,14 +1194,14 @@ namespace MWMechanics
             case ESM::MagicEffect::SummonCreature04:
             case ESM::MagicEffect::SummonCreature05:
             {
-                int actorId = effect.getActorId();
-                if (actorId != -1)
-                    MWBase::Environment::get().getMechanicsManager()->cleanupSummonedCreature(target, actorId);
+                ESM::RefNum actor = effect.getActor();
+                if (actor.isSet())
+                    MWBase::Environment::get().getMechanicsManager()->cleanupSummonedCreature(actor);
                 auto& summons = target.getClass().getCreatureStats(target).getSummonedCreatureMap();
                 auto [begin, end] = summons.equal_range(effect.mEffectId);
                 for (auto it = begin; it != end; ++it)
                 {
-                    if (it->second == actorId)
+                    if (it->second == actor)
                     {
                         summons.erase(it);
                         break;
@@ -1284,7 +1286,7 @@ namespace MWMechanics
                 break;
             case ESM::MagicEffect::AbsorbAttribute:
             {
-                const auto caster = world->searchPtrViaActorId(spellParams.getCasterActorId());
+                const auto caster = worldModel->getPtr(spellParams.getCaster());
                 restoreAttribute(target, effect, effect.mMagnitude);
                 if (!caster.isEmpty())
                     fortifyAttribute(caster, effect, -effect.mMagnitude);
@@ -1294,7 +1296,7 @@ namespace MWMechanics
             {
                 if (target.getClass().isNpc())
                     restoreSkill(target, effect, effect.mMagnitude);
-                const auto caster = world->searchPtrViaActorId(spellParams.getCasterActorId());
+                const auto caster = worldModel->getPtr(spellParams.getCaster());
                 if (!caster.isEmpty() && caster.getClass().isNpc())
                     fortifySkill(caster, effect, -effect.mMagnitude);
             }
diff --git a/apps/openmw/mwmechanics/spellpriority.cpp b/apps/openmw/mwmechanics/spellpriority.cpp
index 7041254c4e..1e811a0658 100644
--- a/apps/openmw/mwmechanics/spellpriority.cpp
+++ b/apps/openmw/mwmechanics/spellpriority.cpp
@@ -82,10 +82,10 @@ namespace
 
     bool isSpellActive(const MWWorld::Ptr& caster, const MWWorld::Ptr& target, const ESM::RefId& id)
     {
-        int actorId = caster.getClass().getCreatureStats(caster).getActorId();
+        ESM::RefNum actor = caster.getCellRef().getRefNum();
         const auto& active = target.getClass().getCreatureStats(target).getActiveSpells();
         return std::find_if(active.begin(), active.end(), [&](const auto& spell) {
-            return spell.getCasterActorId() == actorId && spell.getSourceSpellId() == id;
+            return spell.getCaster() == actor && spell.getSourceSpellId() == id;
         }) != active.end();
     }
 
diff --git a/apps/openmw/mwmechanics/spells.cpp b/apps/openmw/mwmechanics/spells.cpp
index d2baedab0f..f336688c1a 100644
--- a/apps/openmw/mwmechanics/spells.cpp
+++ b/apps/openmw/mwmechanics/spells.cpp
@@ -250,7 +250,7 @@ namespace MWMechanics
 
             // Import data only for player, other actors should not suffer from corprus worsening.
             MWWorld::Ptr player = getPlayer();
-            if (creatureStats->getActorId() != player.getClass().getCreatureStats(player).getActorId())
+            if (creatureStats != &player.getClass().getCreatureStats(player))
                 return;
 
             // Note: if target actor has the Restore attribute effects, stats will be restored.
diff --git a/apps/openmw/mwmechanics/summoning.cpp b/apps/openmw/mwmechanics/summoning.cpp
index 78d4976040..9f7b59b030 100644
--- a/apps/openmw/mwmechanics/summoning.cpp
+++ b/apps/openmw/mwmechanics/summoning.cpp
@@ -13,6 +13,7 @@
 #include "../mwworld/class.hpp"
 #include "../mwworld/esmstore.hpp"
 #include "../mwworld/manualref.hpp"
+#include "../mwworld/worldmodel.hpp"
 
 #include "../mwrender/animation.hpp"
 
@@ -80,10 +81,10 @@ namespace MWMechanics
         return ESM::RefId();
     }
 
-    int summonCreature(int effectId, const MWWorld::Ptr& summoner)
+    ESM::RefNum summonCreature(int effectId, const MWWorld::Ptr& summoner)
     {
         const ESM::RefId& creatureID = getSummonedCreature(effectId);
-        int creatureActorId = -1;
+        ESM::RefNum creature;
         if (!creatureID.empty())
         {
             try
@@ -91,13 +92,12 @@ namespace MWMechanics
                 auto world = MWBase::Environment::get().getWorld();
                 MWWorld::ManualRef ref(world->getStore(), creatureID, 1);
                 MWWorld::Ptr placed = world->safePlaceObject(ref.getPtr(), summoner, summoner.getCell(), 0, 120.f);
-
-                MWMechanics::CreatureStats& summonedCreatureStats = placed.getClass().getCreatureStats(placed);
+                MWBase::Environment::get().getWorldModel()->registerPtr(placed);
+                creature = placed.getCellRef().getRefNum();
 
                 // Make the summoned creature follow its master and help in fights
                 AiFollow package(summoner);
-                summonedCreatureStats.getAiSequence().stack(package, placed);
-                creatureActorId = summonedCreatureStats.getActorId();
+                placed.getClass().getCreatureStats(placed).getAiSequence().stack(package, placed);
 
                 MWRender::Animation* anim = world->getAnimation(placed);
                 if (anim)
@@ -117,9 +117,9 @@ namespace MWMechanics
                 // log
             }
 
-            summoner.getClass().getCreatureStats(summoner).getSummonedCreatureMap().emplace(effectId, creatureActorId);
+            summoner.getClass().getCreatureStats(summoner).getSummonedCreatureMap().emplace(effectId, creature);
         }
-        return creatureActorId;
+        return creature;
     }
 
     void updateSummons(const MWWorld::Ptr& summoner, bool cleanup)
@@ -127,24 +127,18 @@ namespace MWMechanics
         MWMechanics::CreatureStats& creatureStats = summoner.getClass().getCreatureStats(summoner);
         auto& creatureMap = creatureStats.getSummonedCreatureMap();
 
-        std::vector<int> graveyard = creatureStats.getSummonedCreatureGraveyard();
-        creatureStats.getSummonedCreatureGraveyard().clear();
-
-        for (const int creature : graveyard)
-            MWBase::Environment::get().getMechanicsManager()->cleanupSummonedCreature(summoner, creature);
-
         if (!cleanup)
             return;
 
         for (auto it = creatureMap.begin(); it != creatureMap.end();)
         {
-            if (it->second == -1)
+            if (!it->second.isSet())
             {
                 // Keep the spell effect active if we failed to spawn anything
                 it++;
                 continue;
             }
-            MWWorld::Ptr ptr = MWBase::Environment::get().getWorld()->searchPtrViaActorId(it->second);
+            MWWorld::Ptr ptr = MWBase::Environment::get().getWorldModel()->getPtr(it->second);
             if (!ptr.isEmpty() && ptr.getClass().getCreatureStats(ptr).isDead()
                 && ptr.getClass().getCreatureStats(ptr).isDeathAnimationFinished())
             {
@@ -158,15 +152,15 @@ namespace MWMechanics
         }
     }
 
-    void purgeSummonEffect(const MWWorld::Ptr& summoner, const std::pair<int, int>& summon)
+    void purgeSummonEffect(const MWWorld::Ptr& summoner, const std::pair<int, ESM::RefNum>& summon)
     {
         auto& creatureStats = summoner.getClass().getCreatureStats(summoner);
         creatureStats.getActiveSpells().purge(
             [summon](const auto& spell, const auto& effect) {
-                return effect.mEffectId == summon.first && effect.getActorId() == summon.second;
+                return effect.mEffectId == summon.first && effect.getActor() == summon.second;
             },
             summoner);
 
-        MWBase::Environment::get().getMechanicsManager()->cleanupSummonedCreature(summoner, summon.second);
+        MWBase::Environment::get().getMechanicsManager()->cleanupSummonedCreature(summon.second);
     }
 }
diff --git a/apps/openmw/mwmechanics/summoning.hpp b/apps/openmw/mwmechanics/summoning.hpp
index a341ee6e93..3992f8399f 100644
--- a/apps/openmw/mwmechanics/summoning.hpp
+++ b/apps/openmw/mwmechanics/summoning.hpp
@@ -3,6 +3,9 @@
 
 #include <string_view>
 #include <utility>
+
+#include <components/esm3/refnum.hpp>
+
 namespace ESM
 {
     class RefId;
@@ -18,9 +21,9 @@ namespace MWMechanics
 
     ESM::RefId getSummonedCreature(int effectId);
 
-    void purgeSummonEffect(const MWWorld::Ptr& summoner, const std::pair<int, int>& summon);
+    void purgeSummonEffect(const MWWorld::Ptr& summoner, const std::pair<int, ESM::RefNum>& summon);
 
-    int summonCreature(int effectId, const MWWorld::Ptr& summoner);
+    ESM::RefNum summonCreature(int effectId, const MWWorld::Ptr& summoner);
 
     void updateSummons(const MWWorld::Ptr& summoner, bool cleanup);
 }
diff --git a/apps/openmw/mwscript/aiextensions.cpp b/apps/openmw/mwscript/aiextensions.cpp
index 55717a4a5d..7daece407e 100644
--- a/apps/openmw/mwscript/aiextensions.cpp
+++ b/apps/openmw/mwscript/aiextensions.cpp
@@ -124,7 +124,7 @@ namespace MWScript
                 if (!ptr.getClass().isActor() || ptr == MWMechanics::getPlayer())
                     return;
 
-                MWMechanics::AiEscort escortPackage(actorID, static_cast<int>(duration), x, y, z, repeat);
+                MWMechanics::AiEscort escortPackage(actorID, {}, static_cast<int>(duration), x, y, z, repeat);
                 ptr.getClass().getCreatureStats(ptr).getAiSequence().stack(escortPackage, ptr);
 
                 Log(Debug::Info) << "AiEscort: " << x << ", " << y << ", " << z << ", " << duration;
@@ -353,7 +353,7 @@ namespace MWScript
                 if (!ptr.getClass().isActor() || ptr == MWMechanics::getPlayer())
                     return;
 
-                MWMechanics::AiFollow followPackage(actorID, duration, x, y, z, repeat);
+                MWMechanics::AiFollow followPackage(actorID, {}, duration, x, y, z, repeat);
                 ptr.getClass().getCreatureStats(ptr).getAiSequence().stack(followPackage, ptr);
 
                 Log(Debug::Info) << "AiFollow: " << actorID << ", " << x << ", " << y << ", " << z << ", " << duration;
diff --git a/apps/openmw/mwstate/statemanagerimp.cpp b/apps/openmw/mwstate/statemanagerimp.cpp
index dbb4c46ee3..97a516f635 100644
--- a/apps/openmw/mwstate/statemanagerimp.cpp
+++ b/apps/openmw/mwstate/statemanagerimp.cpp
@@ -6,6 +6,7 @@
 
 #include <components/debug/debuglog.hpp>
 
+#include <components/esm3/actoridconverter.hpp>
 #include <components/esm3/esmreader.hpp>
 #include <components/esm3/esmwriter.hpp>
 #include <components/esm3/loadcell.hpp>
@@ -65,7 +66,6 @@ void MWState::StateManager::cleanup(bool force)
         mCharacterManager.setCurrentCharacter(nullptr);
         mTimePlayed = 0;
         mLastSavegame.clear();
-        MWMechanics::CreatureStats::cleanup();
 
         mState = State_NoGame;
         MWBase::Environment::get().getLuaManager()->noGame();
@@ -469,6 +469,10 @@ void MWState::StateManager::loadGame(const Character* character, const std::file
         reader.setContentFileMapping(&contentFileMap);
         MWBase::Environment::get().getLuaManager()->setContentFileMapping(contentFileMap);
 
+        ESM::ActorIdConverter actorIdConverter;
+        if (version <= ESM::MaxActorIdSaveGameFormatVersion)
+            reader.setActorIdConverter(&actorIdConverter);
+
         Loading::Listener& listener = *MWBase::Environment::get().getWindowManager()->getLoadingScreen();
 
         listener.setProgressRange(100);
@@ -589,7 +593,6 @@ void MWState::StateManager::loadGame(const Character* character, const std::file
                 currentPercent = progressPercent;
             }
         }
-
         mCharacterManager.setCurrentCharacter(character);
 
         mState = State_Running;
@@ -599,7 +602,8 @@ void MWState::StateManager::loadGame(const Character* character, const std::file
         mLastSavegame = filepath;
 
         MWBase::Environment::get().getWindowManager()->setNewGame(false);
-        MWBase::Environment::get().getWorld()->saveLoaded();
+        MWBase::Environment::get().getWorld()->saveLoaded(reader);
+        actorIdConverter.apply();
         MWBase::Environment::get().getWorld()->setupPlayer();
         MWBase::Environment::get().getWorld()->renderPlayer();
         MWBase::Environment::get().getWindowManager()->updatePlayer();
@@ -646,6 +650,12 @@ void MWState::StateManager::loadGame(const Character* character, const std::file
         MWBase::Environment::get().getWorldScene()->markCellAsUnchanged();
 
         MWBase::Environment::get().getLuaManager()->gameLoaded();
+        for (int actorId : actorIdConverter.mGraveyard)
+        {
+            auto mapped = actorIdConverter.mMappings.find(actorId);
+            if (mapped != actorIdConverter.mMappings.end())
+                MWBase::Environment::get().getMechanicsManager()->cleanupSummonedCreature(mapped->second);
+        }
     }
     catch (const SaveVersionTooNewError& e)
     {
diff --git a/apps/openmw/mwworld/cellstore.cpp b/apps/openmw/mwworld/cellstore.cpp
index 75ee14f627..d2c7b4af97 100644
--- a/apps/openmw/mwworld/cellstore.cpp
+++ b/apps/openmw/mwworld/cellstore.cpp
@@ -7,6 +7,7 @@
 #include <components/debug/debuglog.hpp>
 
 #include <components/esm/format.hpp>
+#include <components/esm3/actoridconverter.hpp>
 #include <components/esm3/cellref.hpp>
 #include <components/esm3/cellstate.hpp>
 #include <components/esm3/containerstate.hpp>
@@ -141,25 +142,6 @@ namespace
         return MWWorld::Ptr();
     }
 
-    template <typename T>
-    MWWorld::Ptr searchViaActorId(MWWorld::CellRefList<T>& actorList, int actorId, MWWorld::CellStore* cell,
-        const std::map<MWWorld::LiveCellRefBase*, MWWorld::CellStore*>& toIgnore)
-    {
-        for (typename MWWorld::CellRefList<T>::List::iterator iter(actorList.mList.begin());
-             iter != actorList.mList.end(); ++iter)
-        {
-            MWWorld::Ptr actor(&*iter, cell);
-
-            if (toIgnore.find(&*iter) != toIgnore.end())
-                continue;
-
-            if (actor.getClass().getCreatureStats(actor).matchesActorId(actorId) && actor.getCellRef().getCount() > 0)
-                return actor;
-        }
-
-        return MWWorld::Ptr();
-    }
-
     template <typename T>
     void writeReferenceCollection(ESM::ESMWriter& writer, const MWWorld::CellRefList<T>& collection)
     {
@@ -275,6 +257,14 @@ namespace
             if constexpr (std::is_same_v<T, ESM::Creature> || std::is_same_v<T, ESM::NPC>)
                 MWWorld::convertEnchantmentSlots(state.mCreatureStats, state.mInventory);
         }
+        if constexpr (std::is_same_v<T, ESM::Creature> || std::is_same_v<T, ESM::NPC>)
+        {
+            if (reader.getActorIdConverter() && state.mHasCustomState)
+            {
+                MWBase::Environment::get().getWorldModel()->assignSaveFileRefNum(state.mRef);
+                reader.getActorIdConverter()->mMappings.emplace(state.mCreatureStats.mActorId, state.mRef.mRefNum);
+            }
+        }
 
         if (state.mRef.mRefNum.hasContentFile())
         {
@@ -685,26 +675,6 @@ namespace MWWorld
         return searchVisitor.mFound;
     }
 
-    Ptr CellStore::searchViaActorId(int id)
-    {
-        if (Ptr ptr = ::searchViaActorId(get<ESM::NPC>(), id, this, mMovedToAnotherCell); !ptr.isEmpty())
-            return ptr;
-
-        if (Ptr ptr = ::searchViaActorId(get<ESM::Creature>(), id, this, mMovedToAnotherCell); !ptr.isEmpty())
-            return ptr;
-
-        for (const auto& [base, _] : mMovedHere)
-        {
-            MWWorld::Ptr actor(base, this);
-            if (!actor.getClass().isActor())
-                continue;
-            if (actor.getClass().getCreatureStats(actor).matchesActorId(id) && actor.getCellRef().getCount() > 0)
-                return actor;
-        }
-
-        return Ptr();
-    }
-
     class RefNumSearchVisitor
     {
         ESM::RefNum mRefNum;
@@ -1362,20 +1332,6 @@ namespace MWWorld
                 ptr.getBase(), static_cast<float>(MWMechanics::getEnchantmentCharge(*enchantment)));
     }
 
-    Ptr MWWorld::CellStore::getMovedActor(int actorId) const
-    {
-        for (const auto& [cellRef, cell] : mMovedToAnotherCell)
-        {
-            if (cellRef->mClass->isActor() && cellRef->mData.getCustomData())
-            {
-                Ptr actor(cellRef, cell);
-                if (actor.getClass().getCreatureStats(actor).getActorId() == actorId)
-                    return actor;
-            }
-        }
-        return {};
-    }
-
     CellStore* MWWorld::CellStore::getOriginCell(const Ptr& object) const
     {
         MovedRefTracker::const_iterator found = mMovedHere.find(object.getBase());
diff --git a/apps/openmw/mwworld/cellstore.hpp b/apps/openmw/mwworld/cellstore.hpp
index 59127d6186..bca2c137d7 100644
--- a/apps/openmw/mwworld/cellstore.hpp
+++ b/apps/openmw/mwworld/cellstore.hpp
@@ -183,9 +183,6 @@ namespace MWWorld
         /// containers.
         /// @note Does not trigger CellStore hasState flag.
 
-        Ptr searchViaActorId(int id);
-        ///< Will return an empty Ptr if cell is not loaded.
-
         float getWaterLevel() const;
 
         bool movedHere(const MWWorld::Ptr& ptr) const;
@@ -336,8 +333,6 @@ namespace MWWorld
         void respawn();
         ///< Check mLastRespawn and respawn references if necessary. This is a no-op if the cell is not loaded.
 
-        Ptr getMovedActor(int actorId) const;
-
         CellStore* getOriginCell(const Ptr& object) const;
 
         Ptr getPtr(ESM::RefId id);
diff --git a/apps/openmw/mwworld/magiceffects.cpp b/apps/openmw/mwworld/magiceffects.cpp
index 6323dcb772..ff38d909ae 100644
--- a/apps/openmw/mwworld/magiceffects.cpp
+++ b/apps/openmw/mwworld/magiceffects.cpp
@@ -61,7 +61,7 @@ namespace MWWorld
             ESM::ActiveSpells::ActiveSpellParams params;
             params.mSourceSpellId = id;
             params.mDisplayName = spell->mName;
-            params.mCasterActorId = creatureStats.mActorId;
+            params.mCaster.mIndex = creatureStats.mActorId;
             if (spell->mData.mType == ESM::Spell::ST_Ability)
                 params.mFlags = ESM::Compatibility::ActiveSpells::Type_Ability_Flags;
             else
@@ -137,7 +137,7 @@ namespace MWWorld
             ESM::ActiveSpells::ActiveSpellParams params;
             params.mSourceSpellId = id;
             params.mDisplayName = std::move(name);
-            params.mCasterActorId = creatureStats.mActorId;
+            params.mCaster.mIndex = creatureStats.mActorId;
             params.mFlags = ESM::Compatibility::ActiveSpells::Type_Enchantment_Flags;
             params.mWorsenings = -1;
             params.mNextWorsening = ESM::TimeStamp();
@@ -196,7 +196,7 @@ namespace MWWorld
                     {
                         if (effect.mEffectId == key.mEffectId && effect.mEffectIndex == key.mEffectIndex)
                         {
-                            effect.mArg = actorId;
+                            effect.mArg = ESM::RefNum{ .mIndex = static_cast<uint32_t>(actorId), .mContentFile = -1 };
                             effect.mFlags |= ESM::ActiveEffect::Flag_Applied | ESM::ActiveEffect::Flag_Remove;
                             found = true;
                             break;
diff --git a/apps/openmw/mwworld/player.cpp b/apps/openmw/mwworld/player.cpp
index 7bbc469e07..7fa88b5784 100644
--- a/apps/openmw/mwworld/player.cpp
+++ b/apps/openmw/mwworld/player.cpp
@@ -5,6 +5,7 @@
 #include <components/debug/debuglog.hpp>
 
 #include <components/esm/defs.hpp>
+#include <components/esm3/actoridconverter.hpp>
 #include <components/esm3/esmreader.hpp>
 #include <components/esm3/esmwriter.hpp>
 #include <components/esm3/loadbsgn.hpp>
@@ -343,6 +344,9 @@ namespace MWWorld
 
             MWBase::Environment::get().getWorldModel()->deregisterLiveCellRef(mPlayer);
             mPlayer.load(player.mObject);
+            MWBase::Environment::get().getWorldModel()->registerPtr(getPlayer());
+            if (ESM::ActorIdConverter* converter = reader.getActorIdConverter())
+                converter->mMappings.emplace(player.mObject.mCreatureStats.mActorId, mPlayer.mRef.getRefNum());
 
             for (size_t i = 0; i < mSaveAttributes.size(); ++i)
                 mSaveAttributes[i] = player.mSaveAttributes[i];
diff --git a/apps/openmw/mwworld/projectilemanager.cpp b/apps/openmw/mwworld/projectilemanager.cpp
index 203444fa61..c79c265e38 100644
--- a/apps/openmw/mwworld/projectilemanager.cpp
+++ b/apps/openmw/mwworld/projectilemanager.cpp
@@ -9,6 +9,8 @@
 
 #include <components/debug/debuglog.hpp>
 
+#include <components/esm3/actoridconverter.hpp>
+#include <components/esm3/esmreader.hpp>
 #include <components/esm3/esmwriter.hpp>
 #include <components/esm3/loadench.hpp>
 #include <components/esm3/loadmgef.hpp>
@@ -36,6 +38,7 @@
 #include "../mwworld/esmstore.hpp"
 #include "../mwworld/inventorystore.hpp"
 #include "../mwworld/manualref.hpp"
+#include "../mwworld/worldmodel.hpp"
 
 #include "../mwbase/environment.hpp"
 #include "../mwbase/soundmanager.hpp"
@@ -289,10 +292,8 @@ namespace MWWorld
         state.mSpellId = spellId;
         state.mCasterHandle = caster;
         state.mItem = item;
-        if (caster.getClass().isActor())
-            state.mActorId = caster.getClass().getCreatureStats(caster).getActorId();
-        else
-            state.mActorId = -1;
+        MWBase::Environment::get().getWorldModel()->registerPtr(caster);
+        state.mCaster = caster.getCellRef().getRefNum();
 
         std::string texture;
 
@@ -342,7 +343,7 @@ namespace MWWorld
         const osg::Quat& orient, const Ptr& bow, float speed, float attackStrength)
     {
         ProjectileState state;
-        state.mActorId = actor.getClass().getCreatureStats(actor).getActorId();
+        state.mCaster = actor.getCellRef().getRefNum();
         state.mBowId = bow.getCellRef().getRefId();
         state.mVelocity = orient * osg::Vec3f(0, 1, 0) * speed;
         state.mIdArrow = projectile.getCellRef().getRefId();
@@ -367,24 +368,24 @@ namespace MWWorld
     void ProjectileManager::updateCasters()
     {
         for (auto& state : mProjectiles)
-            mPhysics->setCaster(state.mProjectileId, state.getCaster());
+        {
+            state.mCasterHandle = state.getCaster();
+            mPhysics->setCaster(state.mProjectileId, state.mCasterHandle);
+        }
 
         for (auto& state : mMagicBolts)
         {
-            // casters are identified by actor id in the savegame. objects doesn't have one so they can't be identified
-            // back.
-            // TODO: should object-type caster be restored from savegame?
-            if (state.mActorId == -1)
+            if (!state.mCaster.isSet())
                 continue;
 
-            auto caster = state.getCaster();
-            if (caster.isEmpty())
+            state.mCasterHandle = state.getCaster();
+            if (state.mCasterHandle.isEmpty())
             {
-                Log(Debug::Error) << "Couldn't find caster with ID " << state.mActorId;
+                Log(Debug::Error) << "Couldn't find caster with ID " << state.mCaster;
                 cleanupMagicBolt(state);
                 continue;
             }
-            mPhysics->setCaster(state.mProjectileId, caster);
+            mPhysics->setCaster(state.mProjectileId, state.mCasterHandle);
         }
     }
 
@@ -650,37 +651,37 @@ namespace MWWorld
 
     void ProjectileManager::write(ESM::ESMWriter& writer, Loading::Listener& progress) const
     {
-        for (std::vector<ProjectileState>::const_iterator it = mProjectiles.begin(); it != mProjectiles.end(); ++it)
+        for (const ProjectileState& projectile : mProjectiles)
         {
             writer.startRecord(ESM::REC_PROJ);
 
             ESM::ProjectileState state;
-            state.mId = it->mIdArrow;
-            state.mPosition = ESM::Vector3(osg::Vec3f(it->mNode->getPosition()));
-            state.mOrientation = ESM::Quaternion(osg::Quat(it->mNode->getAttitude()));
-            state.mActorId = it->mActorId;
+            state.mId = projectile.mIdArrow;
+            state.mPosition = ESM::Vector3(osg::Vec3f(projectile.mNode->getPosition()));
+            state.mOrientation = ESM::Quaternion(osg::Quat(projectile.mNode->getAttitude()));
+            state.mCaster = projectile.mCaster;
 
-            state.mBowId = it->mBowId;
-            state.mVelocity = it->mVelocity;
-            state.mAttackStrength = it->mAttackStrength;
+            state.mBowId = projectile.mBowId;
+            state.mVelocity = projectile.mVelocity;
+            state.mAttackStrength = projectile.mAttackStrength;
 
             state.save(writer);
 
             writer.endRecord(ESM::REC_PROJ);
         }
 
-        for (std::vector<MagicBoltState>::const_iterator it = mMagicBolts.begin(); it != mMagicBolts.end(); ++it)
+        for (const MagicBoltState& bolt : mMagicBolts)
         {
             writer.startRecord(ESM::REC_MPRJ);
 
             ESM::MagicBoltState state;
-            state.mId = it->mIdMagic.at(0);
-            state.mPosition = ESM::Vector3(osg::Vec3f(it->mNode->getPosition()));
-            state.mOrientation = ESM::Quaternion(osg::Quat(it->mNode->getAttitude()));
-            state.mActorId = it->mActorId;
-            state.mItem = it->mItem;
-            state.mSpellId = it->mSpellId;
-            state.mSpeed = it->mSpeed;
+            state.mId = bolt.mIdMagic.at(0);
+            state.mPosition = ESM::Vector3(osg::Vec3f(bolt.mNode->getPosition()));
+            state.mOrientation = ESM::Quaternion(osg::Quat(bolt.mNode->getAttitude()));
+            state.mCaster = bolt.mCaster;
+            state.mItem = bolt.mItem;
+            state.mSpellId = bolt.mSpellId;
+            state.mSpeed = bolt.mSpeed;
 
             state.save(writer);
 
@@ -696,7 +697,7 @@ namespace MWWorld
             esm.load(reader);
 
             ProjectileState state;
-            state.mActorId = esm.mActorId;
+            state.mCaster = esm.mCaster;
             state.mBowId = esm.mBowId;
             state.mVelocity = esm.mVelocity;
             state.mIdArrow = esm.mId;
@@ -736,7 +737,7 @@ namespace MWWorld
             MagicBoltState state;
             state.mIdMagic.push_back(esm.mId);
             state.mSpellId = esm.mSpellId;
-            state.mActorId = esm.mActorId;
+            state.mCaster = esm.mCaster;
             state.mToDelete = false;
             state.mItem = esm.mItem;
             std::string texture;
@@ -798,12 +799,24 @@ namespace MWWorld
         return mMagicBolts.size() + mProjectiles.size();
     }
 
+    void ProjectileManager::saveLoaded(const ESM::ESMReader& reader)
+    {
+        // Can't do this in readRecord because the vectors might get reallocated as they grow
+        if (reader.getActorIdConverter())
+        {
+            for (ProjectileState& projectile : mProjectiles)
+                reader.getActorIdConverter()->convert(projectile.mCaster, projectile.mCaster.mIndex);
+            for (MagicBoltState& bolt : mMagicBolts)
+                reader.getActorIdConverter()->convert(bolt.mCaster, bolt.mCaster.mIndex);
+        }
+    }
+
     MWWorld::Ptr ProjectileManager::State::getCaster()
     {
         if (!mCasterHandle.isEmpty())
             return mCasterHandle;
 
-        return MWBase::Environment::get().getWorld()->searchPtrViaActorId(mActorId);
+        return MWBase::Environment::get().getWorldModel()->getPtr(mCaster);
     }
 
 }
diff --git a/apps/openmw/mwworld/projectilemanager.hpp b/apps/openmw/mwworld/projectilemanager.hpp
index 432f463dbd..dd26f1df91 100644
--- a/apps/openmw/mwworld/projectilemanager.hpp
+++ b/apps/openmw/mwworld/projectilemanager.hpp
@@ -68,6 +68,7 @@ namespace MWWorld
         void write(ESM::ESMWriter& writer, Loading::Listener& progress) const;
         bool readRecord(ESM::ESMReader& reader, uint32_t type);
         size_t countSavedGameRecords() const;
+        void saveLoaded(const ESM::ESMReader& reader);
 
     private:
         osg::ref_ptr<osg::Group> mParent;
@@ -81,11 +82,7 @@ namespace MWWorld
             osg::ref_ptr<osg::PositionAttitudeTransform> mNode;
             std::shared_ptr<MWRender::EffectAnimationTime> mEffectAnimationTime;
 
-            int mActorId;
-            int mProjectileId;
-
-            // TODO: this will break when the game is saved and reloaded, since there is currently
-            // no way to write identifiers for non-actors to a savegame.
+            ESM::RefNum mCaster;
             MWWorld::Ptr mCasterHandle;
 
             MWWorld::Ptr getCaster();
@@ -96,6 +93,7 @@ namespace MWWorld
             // MW-id of an arrow projectile
             ESM::RefId mIdArrow;
 
+            int mProjectileId;
             bool mToDelete;
         };
 
diff --git a/apps/openmw/mwworld/scene.cpp b/apps/openmw/mwworld/scene.cpp
index a7b9179839..d7b793ae9d 100644
--- a/apps/openmw/mwworld/scene.cpp
+++ b/apps/openmw/mwworld/scene.cpp
@@ -1083,17 +1083,6 @@ namespace MWWorld
         return mActiveCells.contains(&cell);
     }
 
-    Ptr Scene::searchPtrViaActorId(int actorId)
-    {
-        for (CellStoreCollection::const_iterator iter(mActiveCells.begin()); iter != mActiveCells.end(); ++iter)
-        {
-            Ptr ptr = (*iter)->searchViaActorId(actorId);
-            if (!ptr.isEmpty())
-                return ptr;
-        }
-        return Ptr();
-    }
-
     class PreloadMeshItem : public SceneUtil::WorkItem
     {
     public:
diff --git a/apps/openmw/mwworld/scene.hpp b/apps/openmw/mwworld/scene.hpp
index 1fa7779e51..2e81325eab 100644
--- a/apps/openmw/mwworld/scene.hpp
+++ b/apps/openmw/mwworld/scene.hpp
@@ -197,8 +197,6 @@ namespace MWWorld
 
         bool isCellActive(const CellStore& cell);
 
-        Ptr searchPtrViaActorId(int actorId);
-
         void preload(const std::string& mesh, bool useAnim = false);
 
         void testExteriorCells();
diff --git a/apps/openmw/mwworld/worldimp.cpp b/apps/openmw/mwworld/worldimp.cpp
index fcb479db45..94bfaa3997 100644
--- a/apps/openmw/mwworld/worldimp.cpp
+++ b/apps/openmw/mwworld/worldimp.cpp
@@ -449,7 +449,6 @@ namespace MWWorld
             + mGlobalVariables.countSavedGameRecords() + mProjectileManager->countSavedGameRecords()
             + 1 // player record
             + 1 // weather record
-            + 1 // actorId counter
             + 1 // levitation/teleport enabled state
             + 1 // camera
             + 1; // random state.
@@ -472,8 +471,6 @@ namespace MWWorld
             MWBase::Environment::get().getWindowManager()->writeFog(cellstore);
         }
 
-        MWMechanics::CreatureStats::writeActorIdCounter(writer);
-
         mStore.write(writer, progress); // dynamic Store must be written (and read) before Cells, so that
                                         // references to custom made records will be recognized
         mWorldModel.write(writer, progress); // the player's cell needs to be loaded before the player
@@ -497,7 +494,7 @@ namespace MWWorld
         switch (type)
         {
             case ESM::REC_ACTC:
-                MWMechanics::CreatureStats::readActorIdCounter(reader);
+                reader.skipRecord();
                 return;
             case ESM::REC_ENAB:
                 reader.getHNT(mTeleportEnabled, "TELE");
@@ -750,15 +747,6 @@ namespace MWWorld
         throw std::runtime_error(error);
     }
 
-    Ptr World::searchPtrViaActorId(int actorId)
-    {
-        // The player is not registered in any CellStore so must be checked manually
-        if (actorId == getPlayerPtr().getClass().getCreatureStats(getPlayerPtr()).getActorId())
-            return getPlayerPtr();
-        // Now search cells
-        return mWorldScene->searchPtrViaActorId(actorId);
-    }
-
     struct FindContainerVisitor
     {
         ConstPtr mContainedPtr;
@@ -2307,11 +2295,12 @@ namespace MWWorld
         return true;
     }
 
-    void World::saveLoaded()
+    void World::saveLoaded(const ESM::ESMReader& reader)
     {
         mStore.rebuildIdsIndex();
         mStore.validateDynamic();
         mTimeManager->setup(mGlobalVariables);
+        mProjectileManager->saveLoaded(reader);
     }
 
     void World::setupPlayer()
diff --git a/apps/openmw/mwworld/worldimp.hpp b/apps/openmw/mwworld/worldimp.hpp
index 4b8d5def1b..9962978485 100644
--- a/apps/openmw/mwworld/worldimp.hpp
+++ b/apps/openmw/mwworld/worldimp.hpp
@@ -288,9 +288,6 @@ namespace MWWorld
         ///< Return a pointer to a liveCellRef with the given name.
         /// \param activeOnly do not search inactive cells.
 
-        Ptr searchPtrViaActorId(int actorId) override;
-        ///< Search is limited to the active cells.
-
         MWWorld::Ptr findContainer(const MWWorld::ConstPtr& ptr) override;
         ///< Return a pointer to a liveCellRef which contains \a ptr.
         /// \note Search is limited to the active cells.
@@ -467,7 +464,7 @@ namespace MWWorld
         void applyDeferredPreviewRotationToPlayer(float dt) override;
         void disableDeferredPreviewRotation() override;
 
-        void saveLoaded() override;
+        void saveLoaded(const ESM::ESMReader& reader) override;
 
         void setupPlayer() override;
         void renderPlayer() override;
diff --git a/components/CMakeLists.txt b/components/CMakeLists.txt
index 76d4722614..76a94a95db 100644
--- a/components/CMakeLists.txt
+++ b/components/CMakeLists.txt
@@ -189,7 +189,7 @@ add_component_dir (esm3
     weatherstate quickkeys fogstate spellstate activespells creaturelevliststate doorstate projectilestate debugprofile
     aisequence magiceffects custommarkerstate stolenitems transport animationstate controlsstate mappings readerscache
     infoorder timestamp formatversion landrecorddata selectiongroup dialoguecondition
-    refnum
+    refnum actoridconverter
     )
 
 add_component_dir (esmterrain
diff --git a/components/esm3/activespells.cpp b/components/esm3/activespells.cpp
index 7c84afe489..ea6c4fe8ea 100644
--- a/components/esm3/activespells.cpp
+++ b/components/esm3/activespells.cpp
@@ -70,25 +70,6 @@ namespace ESM
             return false;
         }
 
-        struct ToInt
-        {
-            int effectId;
-
-            int operator()(const ESM::RefId& id) const
-            {
-                if (!id.empty())
-                {
-                    if (affectsAttribute(effectId))
-                        return ESM::Attribute::refIdToIndex(id);
-                    else if (affectsSkill(effectId))
-                        return ESM::Skill::refIdToIndex(id);
-                }
-                return -1;
-            }
-
-            int operator()(int actor) const { return actor; }
-        };
-
         void saveImpl(ESMWriter& esm, const std::vector<ActiveSpells::ActiveSpellParams>& spells, NAME tag)
         {
             for (const auto& params : spells)
@@ -96,7 +77,7 @@ namespace ESM
                 esm.writeHNRefId(tag, params.mSourceSpellId);
                 esm.writeHNRefId("SPID", params.mActiveSpellId);
 
-                esm.writeHNT("CAST", params.mCasterActorId);
+                esm.writeFormId(params.mCaster, true, "CAST");
                 esm.writeHNString("DISP", params.mDisplayName);
                 esm.writeHNT("FLAG", params.mFlags);
                 if (params.mItem.isSet())
@@ -110,9 +91,16 @@ namespace ESM
                 for (auto& effect : params.mEffects)
                 {
                     esm.writeHNT("MGEF", effect.mEffectId);
-                    int arg = std::visit(ToInt{ effect.mEffectId }, effect.mArg);
-                    if (arg != -1)
-                        esm.writeHNT("ARG_", arg);
+                    if (const ESM::RefId* id = std::get_if<ESM::RefId>(&effect.mArg))
+                    {
+                        if (!id->empty())
+                            esm.writeHNRefId("ARG_", *id);
+                    }
+                    else if (const ESM::RefNum* actor = std::get_if<ESM::RefNum>(&effect.mArg))
+                    {
+                        if (actor->isSet())
+                            esm.writeFormId(*actor, true, "SUM_");
+                    }
                     esm.writeHNT("MAGN", effect.mMagnitude);
                     esm.writeHNT("MAGN", effect.mMinMagnitude);
                     esm.writeHNT("MAGN", effect.mMaxMagnitude);
@@ -134,7 +122,10 @@ namespace ESM
                 params.mSourceSpellId = esm.getRefId();
                 if (format > MaxActiveSpellTypeVersion)
                     params.mActiveSpellId = esm.getHNRefId("SPID");
-                esm.getHNT(params.mCasterActorId, "CAST");
+                if (format <= MaxActorIdSaveGameFormatVersion)
+                    esm.getHNT(params.mCaster.mIndex, "CAST");
+                else
+                    params.mCaster = esm.getFormId(true, "CAST");
                 params.mDisplayName = esm.getHNString("DISP");
                 if (format <= MaxClearModifiersFormatVersion)
                     params.mFlags = Compatibility::ActiveSpells::Type_Temporary_Flags;
@@ -186,17 +177,24 @@ namespace ESM
                 {
                     ActiveEffect effect;
                     esm.getHT(effect.mEffectId);
-                    int32_t arg = -1;
-                    esm.getHNOT(arg, "ARG_");
-                    if (arg >= 0)
+                    if (format <= MaxActorIdSaveGameFormatVersion)
                     {
-                        if (isSummon(effect.mEffectId))
-                            effect.mArg = arg;
-                        else if (affectsAttribute(effect.mEffectId))
-                            effect.mArg = ESM::Attribute::indexToRefId(arg);
-                        else if (affectsSkill(effect.mEffectId))
-                            effect.mArg = ESM::Skill::indexToRefId(arg);
+                        int32_t arg = -1;
+                        esm.getHNOT(arg, "ARG_");
+                        if (arg >= 0)
+                        {
+                            if (isSummon(effect.mEffectId))
+                                effect.mArg = RefNum{ .mIndex = static_cast<uint32_t>(arg), .mContentFile = -1 };
+                            else if (affectsAttribute(effect.mEffectId))
+                                effect.mArg = ESM::Attribute::indexToRefId(arg);
+                            else if (affectsSkill(effect.mEffectId))
+                                effect.mArg = ESM::Skill::indexToRefId(arg);
+                        }
                     }
+                    else if (esm.peekNextSub("ARG_"))
+                        effect.mArg = esm.getHNRefId("ARG_");
+                    else if (esm.peekNextSub("SUM_"))
+                        effect.mArg = esm.getFormId(true, "SUM_");
                     esm.getHNT(effect.mMagnitude, "MAGN");
                     if (format <= MaxClearModifiersFormatVersion)
                     {
@@ -235,21 +233,22 @@ namespace ESM
 
     void ActiveSpells::load(ESMReader& esm)
     {
+        mActorIdConverter = esm.getActorIdConverter();
         loadImpl(esm, mSpells, "ID__");
         loadImpl(esm, mQueue, "QID_");
     }
 
     RefId ActiveEffect::getSkillOrAttribute() const
     {
-        if (const auto* id = std::get_if<ESM::RefId>(&mArg))
+        if (const ESM::RefId* id = std::get_if<ESM::RefId>(&mArg))
             return *id;
         return {};
     }
 
-    int ActiveEffect::getActorId() const
+    RefNum ActiveEffect::getActor() const
     {
-        if (const auto* id = std::get_if<int>(&mArg))
-            return *id;
-        return -1;
+        if (const ESM::RefNum* actor = std::get_if<ESM::RefNum>(&mArg))
+            return *actor;
+        return {};
     }
 }
diff --git a/components/esm3/activespells.hpp b/components/esm3/activespells.hpp
index 3058e8e4de..0db1b0e61b 100644
--- a/components/esm3/activespells.hpp
+++ b/components/esm3/activespells.hpp
@@ -14,6 +14,7 @@ namespace ESM
 {
     class ESMReader;
     class ESMWriter;
+    class ActorIdConverter;
 
     // Parameters of an effect concerning lasting effects.
     // Note we are not using ENAMstruct since the magnitude may be modified by magic resistance, etc.
@@ -34,14 +35,14 @@ namespace ESM
         float mMagnitude;
         float mMinMagnitude;
         float mMaxMagnitude;
-        std::variant<RefId, int> mArg; // skill, attribute, or summon
+        std::variant<RefId, RefNum> mArg; // skill, attribute, or summon
         float mDuration;
         float mTimeLeft;
         int32_t mEffectIndex;
         int32_t mFlags;
 
         RefId getSkillOrAttribute() const;
-        int getActorId() const;
+        RefNum getActor() const;
     };
 
     // format 0, saved games only
@@ -65,7 +66,7 @@ namespace ESM
             RefId mSourceSpellId;
             std::vector<ActiveEffect> mEffects;
             std::string mDisplayName;
-            int32_t mCasterActorId;
+            RefNum mCaster;
             RefNum mItem;
             Flags mFlags;
             int32_t mWorsenings;
@@ -74,6 +75,7 @@ namespace ESM
 
         std::vector<ActiveSpellParams> mSpells;
         std::vector<ActiveSpellParams> mQueue;
+        ActorIdConverter* mActorIdConverter = nullptr;
 
         void load(ESMReader& esm);
         void save(ESMWriter& esm) const;
diff --git a/components/esm3/actoridconverter.cpp b/components/esm3/actoridconverter.cpp
new file mode 100644
index 0000000000..dba9cb82ea
--- /dev/null
+++ b/components/esm3/actoridconverter.cpp
@@ -0,0 +1,32 @@
+#include "actoridconverter.hpp"
+
+namespace ESM
+{
+    void ActorIdConverter::apply()
+    {
+        for (auto& [refNum, actorId] : mToConvert)
+        {
+            auto it = mMappings.find(actorId);
+            if (it == mMappings.end())
+                refNum = {};
+            else
+                refNum = it->second;
+        }
+    }
+
+    void ActorIdConverter::convert(ESM::RefNum& refNum, int actorId)
+    {
+        if (actorId == -1)
+        {
+            refNum = {};
+            return;
+        }
+        auto it = mMappings.find(actorId);
+        if (it == mMappings.end())
+        {
+            mToConvert.emplace_back(refNum, actorId);
+            return;
+        }
+        refNum = it->second;
+    }
+}
diff --git a/components/esm3/actoridconverter.hpp b/components/esm3/actoridconverter.hpp
new file mode 100644
index 0000000000..09b7e71aa1
--- /dev/null
+++ b/components/esm3/actoridconverter.hpp
@@ -0,0 +1,25 @@
+#ifndef OPENMW_COMPONENTS_ESM3_ACTORIDCONVERTER_H
+#define OPENMW_COMPONENTS_ESM3_ACTORIDCONVERTER_H
+
+#include <map>
+#include <vector>
+
+#include "refnum.hpp"
+
+namespace ESM
+{
+    class ActorIdConverter
+    {
+        std::vector<std::pair<ESM::RefNum&, int>> mToConvert;
+
+    public:
+        std::map<int, ESM::RefNum> mMappings;
+        std::vector<int> mGraveyard;
+
+        void apply();
+
+        void convert(ESM::RefNum& refNum, int actorId);
+    };
+}
+
+#endif
diff --git a/components/esm3/aisequence.cpp b/components/esm3/aisequence.cpp
index ba28ca3e92..0ecba5f7cc 100644
--- a/components/esm3/aisequence.cpp
+++ b/components/esm3/aisequence.cpp
@@ -35,6 +35,22 @@ namespace ESM
         f(v.mX, v.mY, v.mZ, v.mDuration);
     }
 
+    namespace
+    {
+        void loadActorId(ESMReader& esm, ESM::NAME name, RefNum& refNum)
+        {
+            if (esm.getFormatVersion() <= MaxActorIdSaveGameFormatVersion)
+            {
+                refNum.mIndex = static_cast<uint32_t>(-1);
+                esm.getHNOT(refNum.mIndex, name);
+            }
+            else if (esm.peekNextSub(name))
+                refNum = esm.getFormId(true, name);
+            else
+                refNum = {};
+        }
+    }
+
     namespace AiSequence
     {
         void AiWander::load(ESMReader& esm)
@@ -72,8 +88,7 @@ namespace ESM
         {
             esm.getNamedComposite("DATA", mData);
             mTargetId = esm.getHNRefId("TARG");
-            mTargetActorId = -1;
-            esm.getHNOT(mTargetActorId, "TAID");
+            loadActorId(esm, "TAID", mTargetActor);
             esm.getHNT(mRemainingDuration, "DURA");
             mCellId = esm.getHNOString("CELL");
             mRepeat = false;
@@ -92,7 +107,8 @@ namespace ESM
         {
             esm.writeNamedComposite("DATA", mData);
             esm.writeHNRefId("TARG", mTargetId);
-            esm.writeHNT("TAID", mTargetActorId);
+            if (esm.getFormatVersion() > MaxActorIdSaveGameFormatVersion)
+                esm.writeFormId(mTargetActor, true, "TAID");
             esm.writeHNT("DURA", mRemainingDuration);
             if (!mCellId.empty())
                 esm.writeHNString("CELL", mCellId);
@@ -104,8 +120,7 @@ namespace ESM
         {
             esm.getNamedComposite("DATA", mData);
             mTargetId = esm.getHNRefId("TARG");
-            mTargetActorId = -1;
-            esm.getHNOT(mTargetActorId, "TAID");
+            loadActorId(esm, "TAID", mTargetActor);
             esm.getHNT(mRemainingDuration, "DURA");
             mCellId = esm.getHNOString("CELL");
             esm.getHNT(mAlwaysFollow, "ALWY");
@@ -129,7 +144,8 @@ namespace ESM
         {
             esm.writeNamedComposite("DATA", mData);
             esm.writeHNRefId("TARG", mTargetId);
-            esm.writeHNT("TAID", mTargetActorId);
+            if (esm.getFormatVersion() > MaxActorIdSaveGameFormatVersion)
+                esm.writeFormId(mTargetActor, true, "TAID");
             esm.writeHNT("DURA", mRemainingDuration);
             if (!mCellId.empty())
                 esm.writeHNString("CELL", mCellId);
@@ -157,22 +173,22 @@ namespace ESM
 
         void AiCombat::load(ESMReader& esm)
         {
-            esm.getHNT(mTargetActorId, "TARG");
+            loadActorId(esm, "TARG", mTargetActor);
         }
 
         void AiCombat::save(ESMWriter& esm) const
         {
-            esm.writeHNT("TARG", mTargetActorId);
+            esm.writeFormId(mTargetActor, true, "TARG");
         }
 
         void AiPursue::load(ESMReader& esm)
         {
-            esm.getHNT(mTargetActorId, "TARG");
+            loadActorId(esm, "TARG", mTargetActor);
         }
 
         void AiPursue::save(ESMWriter& esm) const
         {
-            esm.writeHNT("TARG", mTargetActorId);
+            esm.writeFormId(mTargetActor, true, "TARG");
         }
 
         void AiSequence::save(ESMWriter& esm) const
@@ -214,6 +230,7 @@ namespace ESM
 
         void AiSequence::load(ESMReader& esm)
         {
+            mActorIdConverter = esm.getActorIdConverter();
             int count = 0;
             while (esm.isNextSub("AIPK"))
             {
diff --git a/components/esm3/aisequence.hpp b/components/esm3/aisequence.hpp
index 729a914544..342d4161e9 100644
--- a/components/esm3/aisequence.hpp
+++ b/components/esm3/aisequence.hpp
@@ -9,8 +9,11 @@
 #include <components/esm/refid.hpp>
 #include <components/esm/vector3.hpp>
 
+#include "refnum.hpp"
+
 namespace ESM
 {
+    class ActorIdConverter;
     class ESMReader;
     class ESMWriter;
 
@@ -33,7 +36,7 @@ namespace ESM
 
         struct AiPackage
         {
-            virtual ~AiPackage() {}
+            virtual ~AiPackage() = default;
         };
 
         struct AiWanderData
@@ -89,7 +92,7 @@ namespace ESM
         {
             AiEscortData mData;
 
-            int32_t mTargetActorId;
+            ESM::RefNum mTargetActor;
             ESM::RefId mTargetId;
             std::string mCellId;
             float mRemainingDuration;
@@ -103,7 +106,7 @@ namespace ESM
         {
             AiEscortData mData;
 
-            int32_t mTargetActorId;
+            ESM::RefNum mTargetActor;
             ESM::RefId mTargetId;
             std::string mCellId;
             float mRemainingDuration;
@@ -129,7 +132,7 @@ namespace ESM
 
         struct AiCombat : AiPackage
         {
-            int32_t mTargetActorId;
+            ESM::RefNum mTargetActor;
 
             void load(ESMReader& esm);
             void save(ESMWriter& esm) const;
@@ -137,7 +140,7 @@ namespace ESM
 
         struct AiPursue : AiPackage
         {
-            int32_t mTargetActorId;
+            ESM::RefNum mTargetActor;
 
             void load(ESMReader& esm);
             void save(ESMWriter& esm) const;
@@ -152,17 +155,16 @@ namespace ESM
 
         struct AiSequence
         {
-            AiSequence() { mLastAiPackage = -1; }
-
             std::vector<AiPackageContainer> mPackages;
-            int32_t mLastAiPackage;
+            ActorIdConverter* mActorIdConverter = nullptr;
+            int32_t mLastAiPackage = -1;
+
+            AiSequence() {}
+            AiSequence(const AiSequence&) = delete;
+            AiSequence& operator=(const AiSequence&) = delete;
 
             void load(ESMReader& esm);
             void save(ESMWriter& esm) const;
-
-        private:
-            AiSequence(const AiSequence&);
-            AiSequence& operator=(const AiSequence&);
         };
 
     }
diff --git a/components/esm3/creaturelevliststate.cpp b/components/esm3/creaturelevliststate.cpp
index 6deb7d68b7..7af2f1e2a1 100644
--- a/components/esm3/creaturelevliststate.cpp
+++ b/components/esm3/creaturelevliststate.cpp
@@ -10,8 +10,13 @@ namespace ESM
     {
         ObjectState::load(esm);
 
-        mSpawnActorId = -1;
-        esm.getHNOT(mSpawnActorId, "SPAW");
+        if (esm.getFormatVersion() <= MaxActorIdSaveGameFormatVersion)
+        {
+            mSpawnedActor.mIndex = static_cast<uint32_t>(-1);
+            esm.getHNOT(mSpawnedActor.mIndex, "SPAW");
+        }
+        else if (esm.peekNextSub("SPAW"))
+            mSpawnedActor = esm.getFormId(true, "SPAW");
 
         mSpawn = false;
         esm.getHNOT(mSpawn, "RESP");
@@ -21,8 +26,8 @@ namespace ESM
     {
         ObjectState::save(esm, inInventory);
 
-        if (mSpawnActorId != -1)
-            esm.writeHNT("SPAW", mSpawnActorId);
+        if (mSpawnedActor.isSet())
+            esm.writeFormId(mSpawnedActor, true, "SPAW");
 
         if (mSpawn)
             esm.writeHNT("RESP", mSpawn);
diff --git a/components/esm3/creaturelevliststate.hpp b/components/esm3/creaturelevliststate.hpp
index e7121cf8ac..7b7de481a1 100644
--- a/components/esm3/creaturelevliststate.hpp
+++ b/components/esm3/creaturelevliststate.hpp
@@ -9,7 +9,7 @@ namespace ESM
 
     struct CreatureLevListState final : public ObjectState
     {
-        int32_t mSpawnActorId;
+        ESM::RefNum mSpawnedActor; // actor id in older saves
         bool mSpawn;
 
         void load(ESMReader& esm) override;
diff --git a/components/esm3/creaturestats.cpp b/components/esm3/creaturestats.cpp
index 44c3bd993b..ba61a8c895 100644
--- a/components/esm3/creaturestats.cpp
+++ b/components/esm3/creaturestats.cpp
@@ -118,7 +118,8 @@ namespace ESM
                 int32_t actorId;
                 esm.getHNT(actorId, "ACID");
                 mSummonedCreatureMap[SummonKey(magicEffect, source, effectIndex)] = actorId;
-                mSummonedCreatures.emplace(magicEffect, actorId);
+                mSummonedCreatures.emplace(
+                    magicEffect, RefNum{ .mIndex = static_cast<uint32_t>(actorId), .mContentFile = -1 });
             }
         }
         else
@@ -127,9 +128,12 @@ namespace ESM
             {
                 int32_t magicEffect;
                 esm.getHT(magicEffect);
-                int32_t actorId;
-                esm.getHNT(actorId, "ACID");
-                mSummonedCreatures.emplace(magicEffect, actorId);
+                RefNum actor;
+                if (esm.getFormatVersion() <= MaxActorIdSaveGameFormatVersion)
+                    esm.getHNT(actor.mIndex, "ACID");
+                else
+                    actor = esm.getFormId(true, "ACID");
+                mSummonedCreatures.emplace(magicEffect, actor);
             }
         }
 
@@ -231,9 +235,6 @@ namespace ESM
         if (mLevel != 1)
             esm.writeHNT("LEVL", mLevel);
 
-        if (mActorId != -1)
-            esm.writeHNT("ACID", mActorId);
-
         if (mDeathAnimation != -1)
             esm.writeHNT("DANM", mDeathAnimation);
 
@@ -245,15 +246,10 @@ namespace ESM
         mAiSequence.save(esm);
         mMagicEffects.save(esm);
 
-        for (const auto& [effectId, actorId] : mSummonedCreatures)
+        for (const auto& [effectId, actor] : mSummonedCreatures)
         {
             esm.writeHNT("SUMM", effectId);
-            esm.writeHNT("ACID", actorId);
-        }
-
-        for (int32_t key : mSummonGraveyard)
-        {
-            esm.writeHNT("GRAV", key);
+            esm.writeFormId(actor, true, "ACID");
         }
 
         esm.writeHNT("AISE", mHasAiSettings);
diff --git a/components/esm3/creaturestats.hpp b/components/esm3/creaturestats.hpp
index 6e65a52354..cba74e065d 100644
--- a/components/esm3/creaturestats.hpp
+++ b/components/esm3/creaturestats.hpp
@@ -43,7 +43,7 @@ namespace ESM
         std::array<StatState<int>, 4> mAiSettings;
 
         std::map<SummonKey, int> mSummonedCreatureMap;
-        std::multimap<int, int> mSummonedCreatures;
+        std::multimap<int, RefNum> mSummonedCreatures;
         std::vector<int> mSummonGraveyard;
 
         TimeStamp mTradeTime;
diff --git a/components/esm3/esmreader.hpp b/components/esm3/esmreader.hpp
index 9bae5f217e..938275c69e 100644
--- a/components/esm3/esmreader.hpp
+++ b/components/esm3/esmreader.hpp
@@ -43,6 +43,7 @@ namespace ESM
     inline constexpr bool IsReadable<void> = false;
 
     class ReadersCache;
+    class ActorIdConverter; // For old save games
 
     class ESMReader
     {
@@ -118,11 +119,13 @@ namespace ESM
 
         // Used only when loading saves to adjust FormIds if load order was changes.
         void setContentFileMapping(const std::map<int, int>* mapping) { mContentFileMapping = mapping; }
-        const std::map<int, int>* getContentFileMapping();
 
         // Returns false if content file not found.
         bool applyContentFileMapping(FormId& id);
 
+        void setActorIdConverter(ActorIdConverter* converter) { mActorIdConverter = converter; }
+        ActorIdConverter* getActorIdConverter() const { return mActorIdConverter; }
+
         /*************************************************************************
          *
          *  Medium-level reading shortcuts
@@ -386,6 +389,8 @@ namespace ESM
         size_t mFileSize;
 
         const std::map<int, int>* mContentFileMapping = nullptr;
+
+        ActorIdConverter* mActorIdConverter = nullptr;
     };
 }
 #endif
diff --git a/components/esm3/formatversion.hpp b/components/esm3/formatversion.hpp
index f25cdca4bf..f0cb36465d 100644
--- a/components/esm3/formatversion.hpp
+++ b/components/esm3/formatversion.hpp
@@ -28,7 +28,8 @@ namespace ESM
     inline constexpr FormatVersion MaxOldCountFormatVersion = 30;
     inline constexpr FormatVersion MaxActiveSpellTypeVersion = 31;
     inline constexpr FormatVersion MaxPlayerBeforeCellDataFormatVersion = 32;
-    inline constexpr FormatVersion CurrentSaveGameFormatVersion = 34;
+    inline constexpr FormatVersion MaxActorIdSaveGameFormatVersion = 34;
+    inline constexpr FormatVersion CurrentSaveGameFormatVersion = 35;
 
     inline constexpr FormatVersion MinSupportedSaveGameFormatVersion = 5;
     inline constexpr FormatVersion OpenMW0_49MinSaveGameFormatVersion = 5;
diff --git a/components/esm3/objectstate.cpp b/components/esm3/objectstate.cpp
index f3017e2d0d..6f83e6a648 100644
--- a/components/esm3/objectstate.cpp
+++ b/components/esm3/objectstate.cpp
@@ -14,6 +14,7 @@ namespace ESM
     void ObjectState::load(ESMReader& esm)
     {
         mVersion = esm.getFormatVersion();
+        mActorIdConverter = esm.getActorIdConverter();
 
         bool isDeleted;
         mRef.loadData(esm, isDeleted);
diff --git a/components/esm3/objectstate.hpp b/components/esm3/objectstate.hpp
index c947adcd97..fc8760d333 100644
--- a/components/esm3/objectstate.hpp
+++ b/components/esm3/objectstate.hpp
@@ -14,6 +14,7 @@
 
 namespace ESM
 {
+    class ActorIdConverter;
     class ESMReader;
     class ESMWriter;
     struct ContainerState;
@@ -29,27 +30,18 @@ namespace ESM
     {
         CellRef mRef;
 
-        unsigned char mHasLocals;
         Locals mLocals;
         LuaScripts mLuaScripts;
-        unsigned char mEnabled;
         Position mPosition;
-        uint32_t mFlags;
+        AnimationState mAnimationState;
+        ActorIdConverter* mActorIdConverter = nullptr;
+        FormatVersion mVersion = DefaultFormatVersion;
+        uint32_t mFlags = 0;
+        unsigned char mHasLocals = 0;
+        unsigned char mEnabled = 0;
 
         // Is there any class-specific state following the ObjectState
-        bool mHasCustomState;
-
-        FormatVersion mVersion = DefaultFormatVersion;
-
-        AnimationState mAnimationState;
-
-        ObjectState()
-            : mHasLocals(0)
-            , mEnabled(0)
-            , mFlags(0)
-            , mHasCustomState(true)
-        {
-        }
+        bool mHasCustomState = true;
 
         /// @note Does not load the CellRef ID, it should already be loaded before calling this method
         virtual void load(ESMReader& esm);
diff --git a/components/esm3/projectilestate.cpp b/components/esm3/projectilestate.cpp
index e20cefa882..3b23ff7813 100644
--- a/components/esm3/projectilestate.cpp
+++ b/components/esm3/projectilestate.cpp
@@ -11,7 +11,7 @@ namespace ESM
         esm.writeHNRefId("ID__", mId);
         esm.writeHNT("VEC3", mPosition);
         esm.writeHNT("QUAT", mOrientation);
-        esm.writeHNT("ACTO", mActorId);
+        esm.writeFormId(mCaster, true, "ACTO");
     }
 
     void BaseProjectileState::load(ESMReader& esm)
@@ -19,7 +19,13 @@ namespace ESM
         mId = esm.getHNRefId("ID__");
         esm.getHNT("VEC3", mPosition.mValues);
         esm.getHNT("QUAT", mOrientation.mValues);
-        esm.getHNT(mActorId, "ACTO");
+        if (esm.getFormatVersion() <= MaxActorIdSaveGameFormatVersion)
+        {
+            mCaster.mIndex = static_cast<uint32_t>(-1);
+            esm.getHNT(mCaster.mIndex, "ACTO");
+        }
+        else
+            mCaster = esm.getFormId(true, "ACTO");
     }
 
     void MagicBoltState::save(ESMWriter& esm) const
diff --git a/components/esm3/projectilestate.hpp b/components/esm3/projectilestate.hpp
index c89d55c0e5..4c34ce3ca1 100644
--- a/components/esm3/projectilestate.hpp
+++ b/components/esm3/projectilestate.hpp
@@ -24,7 +24,7 @@ namespace ESM
         Vector3 mPosition;
         Quaternion mOrientation;
 
-        int32_t mActorId;
+        RefNum mCaster;
 
         void load(ESMReader& esm);
         void save(ESMWriter& esm) const;