diff --git a/src/namedef_custom.h b/src/namedef_custom.h
index dbf94dbafc..af61b6499c 100644
--- a/src/namedef_custom.h
+++ b/src/namedef_custom.h
@@ -452,6 +452,7 @@ xx(Readthismenu)
 xx(Playermenu)
 
 // more stuff
+xx(Behavior)
 xx(ColorSet)
 xx(NeverSwitchOnPickup)
 xx(MoveBob)
diff --git a/src/playsim/actor.h b/src/playsim/actor.h
index 2f461e1089..f5bfefb5a9 100644
--- a/src/playsim/actor.h
+++ b/src/playsim/actor.h
@@ -793,6 +793,7 @@ public:
 
 	virtual void OnDestroy() override;
 	virtual void Serialize(FSerializer &arc) override;
+	virtual size_t PropagateMark() override;
 	virtual void PostSerialize() override;
 	virtual void PostBeginPlay() override;		// Called immediately before the actor's first tick
 	virtual void Tick() override;
@@ -1373,6 +1374,7 @@ public:
 	// landing speed from a jump with normal gravity (squats the player's view)
 	// (note: this is put into AActor instead of the PlayerPawn because non-players also use the value)
 	double LandingSpeed;
+	TMap<FName, DObject*> Behaviors;
 
 
 	// ThingIDs
@@ -1434,6 +1436,17 @@ public:
 		return GetClass()->FindState(numnames, names, exact);
 	}
 
+	DObject* FindBehavior(const PClass& type) const
+	{
+		auto b = Behaviors.CheckKey(type.TypeName);
+		return b != nullptr && *b != nullptr && !((*b)->ObjectFlags & OF_EuthanizeMe) ? *b : nullptr;
+	}
+	DObject* AddBehavior(const PClass& type);
+	bool RemoveBehavior(const PClass& type);
+	void TickBehaviors();
+	void MoveBehaviors(AActor& from);
+	void ClearBehaviors();
+
 	bool HasSpecialDeathStates () const;
 
 	double X() const
diff --git a/src/playsim/p_mobj.cpp b/src/playsim/p_mobj.cpp
index 9700118504..743843852f 100644
--- a/src/playsim/p_mobj.cpp
+++ b/src/playsim/p_mobj.cpp
@@ -197,6 +197,22 @@ void AActor::EnableNetworking(const bool enable)
 	Super::EnableNetworking(true);
 }
 
+//==========================================================================
+//
+// AActor :: PropagateMark
+//
+//==========================================================================
+
+size_t AActor::PropagateMark()
+{
+	TMap<FName, DObject*>::Iterator it = { Behaviors };
+	TMap<FName, DObject*>::Pair* pair = nullptr;
+	while (it.NextPair(pair))
+		GC::Mark(pair->Value);
+
+	return Super::PropagateMark();
+}
+
 //==========================================================================
 //
 // AActor :: Serialize
@@ -402,7 +418,8 @@ void AActor::Serialize(FSerializer &arc)
 		("morphflags", MorphFlags)
 		("premorphproperties", PremorphProperties)
 		("morphexitflash", MorphExitFlash)
-		("damagesource", damagesource);
+		("damagesource", damagesource)
+		("behaviors", Behaviors);
 
 
 		SerializeTerrain(arc, "floorterrain", floorterrain, &def->floorterrain);
@@ -444,6 +461,229 @@ void AActor::PostSerialize()
 	UpdateWaterLevel(false);
 }
 
+//==========================================================================
+//
+// Behaviors allow for actions to be defined on Actors not coupled to
+// specific inventory tokens. Only one can be attached at a time.
+//
+//==========================================================================
+
+bool AActor::RemoveBehavior(const PClass& type)
+{
+	if (Behaviors.CheckKey(type.TypeName))
+	{
+		auto b = Behaviors[type.TypeName];
+
+		Behaviors.Remove(type.TypeName);
+		if (b != nullptr && !(b->ObjectFlags & OF_EuthanizeMe))
+		{
+			b->Destroy();
+			return true;
+		}
+	}
+
+	return false;
+}
+
+static int RemoveBehavior(AActor* self, PClass* type)
+{
+	return self->RemoveBehavior(*type);
+}
+
+DEFINE_ACTION_FUNCTION_NATIVE(AActor, RemoveBehavior, RemoveBehavior)
+{
+	PARAM_SELF_PROLOGUE(AActor);
+	PARAM_CLASS_NOT_NULL(type, DObject);
+	ACTION_RETURN_BOOL(self->RemoveBehavior(*type));
+}
+
+DObject* AActor::AddBehavior(const PClass& type)
+{
+	if (type.bAbstract || !type.IsDescendantOf(NAME_Behavior))
+		return nullptr;
+
+	auto b = FindBehavior(type);
+	if (b == nullptr)
+	{
+		b = Create<DObject>();
+		if (b == nullptr)
+			return nullptr;
+
+		auto& owner = b->PointerVar<AActor>(NAME_Owner);
+		owner = this;
+
+		Behaviors[type.TypeName] = b;
+		IFOVERRIDENVIRTUALPTRNAME(b, NAME_Behavior, Initialize)
+		{
+			VMValue params[] = { b };
+			VMCall(func, params, 1, nullptr, 0);
+
+			if (b->ObjectFlags & OF_EuthanizeMe)
+			{
+				RemoveBehavior(type);
+				return nullptr;
+			}
+		}
+	}
+	else
+	{
+		IFOVERRIDENVIRTUALPTRNAME(b, NAME_Behavior, Readded)
+		{
+			VMValue params[] = { b };
+			VMCall(func, params, 1, nullptr, 0);
+
+			if (b->ObjectFlags & OF_EuthanizeMe)
+			{
+				RemoveBehavior(type);
+				return nullptr;
+			}
+		}
+	}
+
+	return b;
+}
+
+static DObject* AddBehavior(AActor* self, PClass* type)
+{
+	return self->AddBehavior(*type);
+}
+
+DEFINE_ACTION_FUNCTION_NATIVE(AActor, AddBehavior, AddBehavior)
+{
+	PARAM_SELF_PROLOGUE(AActor);
+	PARAM_CLASS_NOT_NULL(type, DObject);
+	ACTION_RETURN_OBJECT(self->AddBehavior(*type));
+}
+
+void AActor::TickBehaviors()
+{
+	TArray<FName> toRemove = {};
+
+	TMap<FName, DObject*>::Iterator it = { Behaviors };
+	TMap<FName, DObject*>::Pair* pair = nullptr;
+	while (it.NextPair(pair))
+	{
+		auto b = pair->Value;
+		if (b == nullptr || (b->ObjectFlags & OF_EuthanizeMe))
+		{
+			toRemove.Push(pair->Key);
+			continue;
+		}
+
+		auto& owner = b->PointerVar<AActor>(NAME_Owner);
+		if (owner != this)
+		{
+			toRemove.Push(pair->Key);
+			continue;
+		}
+
+		IFOVERRIDENVIRTUALPTRNAME(b, NAME_Behavior, Tick)
+		{
+			VMValue params[] = { b };
+			VMCall(func, params, 1, nullptr, 0);
+
+			if (b->ObjectFlags & OF_EuthanizeMe)
+				toRemove.Push(pair->Key);
+		}
+	}
+
+	for (auto& type : toRemove)
+		RemoveBehavior(*PClass::FindClass(type));
+}
+
+static void TickBehaviors(AActor* self)
+{
+	self->TickBehaviors();
+}
+
+DEFINE_ACTION_FUNCTION_NATIVE(AActor, TickBehaviors, TickBehaviors)
+{
+	PARAM_SELF_PROLOGUE(AActor);
+	self->TickBehaviors();
+	return 0;
+}
+
+static DObject* FindBehavior(AActor* self, PClass* type)
+{
+	return self->FindBehavior(*type);
+}
+
+DEFINE_ACTION_FUNCTION_NATIVE(AActor, FindBehavior, FindBehavior)
+{
+	PARAM_SELF_PROLOGUE(AActor);
+	PARAM_CLASS_NOT_NULL(type, DObject);
+	ACTION_RETURN_OBJECT(self->FindBehavior(*type));
+}
+
+void AActor::MoveBehaviors(AActor& from)
+{
+	// Clean these up properly before transferring.
+	ClearBehaviors();
+
+	Behaviors.TransferFrom(from.Behaviors);
+
+	TArray<FName> toRemove = {};
+	
+	// Clean up any empty behaviors that remained as well while
+	// changing the owner.
+	TMap<FName, DObject*>::Iterator it = { Behaviors };
+	TMap<FName, DObject*>::Pair* pair = nullptr;
+	while (it.NextPair(pair))
+	{
+		auto b = pair->Value;
+		if (b == nullptr || (b->ObjectFlags & OF_EuthanizeMe))
+		{
+			toRemove.Push(pair->Key);
+			continue;
+		}
+
+		auto owner = b->PointerVar<AActor>(NAME_Owner);
+		owner = this;
+	}
+
+	for (auto& type : toRemove)
+		RemoveBehavior(*PClass::FindClass(type));
+}
+
+static void MoveBehaviors(AActor* self, AActor* from)
+{
+	self->MoveBehaviors(*from);
+}
+
+DEFINE_ACTION_FUNCTION_NATIVE(AActor, MoveBehaviors, MoveBehaviors)
+{
+	PARAM_SELF_PROLOGUE(AActor);
+	PARAM_OBJECT_NOT_NULL(from, AActor);
+	self->MoveBehaviors(*from);
+	return 0;
+}
+
+void AActor::ClearBehaviors()
+{
+	TArray<FName> toRemove = {};
+
+	TMap<FName, DObject*>::Iterator it = { Behaviors };
+	TMap<FName, DObject*>::Pair* pair = nullptr;
+	while (it.NextPair(pair))
+		toRemove.Push(pair->Key);
+
+	for (auto& type : toRemove)
+		RemoveBehavior(*PClass::FindClass(type));
+
+	Behaviors.Clear();
+}
+
+static void ClearBehaviors(AActor* self)
+{
+	self->ClearBehaviors();
+}
+
+DEFINE_ACTION_FUNCTION_NATIVE(AActor, ClearBehaviors, ClearBehaviors)
+{
+	PARAM_SELF_PROLOGUE(AActor);
+	self->ClearBehaviors();
+	return 0;
+}
 
 //==========================================================================
 //
@@ -3931,6 +4171,11 @@ void AActor::Tick ()
 		return;
 	}
 
+	// These should always tick regardless of prediction or not (let the behavior itself
+	// handle this).
+	if (!isFrozen())
+		TickBehaviors();
+
 	if (flags5 & MF5_NOINTERACTION)
 	{
 		// only do the minimally necessary things here to save time:
@@ -5251,6 +5496,9 @@ void AActor::OnDestroy ()
 		Level->localEventManager->WorldThingDestroyed(this);
 	}
 
+	
+	ClearBehaviors();
+
 	DeleteAttachedLights();
 	ClearRenderSectorList();
 	ClearRenderLineList();
@@ -5497,6 +5745,8 @@ int MorphPointerSubstitution(AActor* from, AActor* to)
 		VMCall(func, params, 2, nullptr, 0);
 	}
 
+	to->MoveBehaviors(*from);
+
 	// Go through player infos.
 	for (int i = 0; i < MAXPLAYERS; ++i)
 	{
diff --git a/src/serializer_doom.cpp b/src/serializer_doom.cpp
index 2ec1c8b861..a46d8c3f3b 100644
--- a/src/serializer_doom.cpp
+++ b/src/serializer_doom.cpp
@@ -226,6 +226,33 @@ FSerializer& FDoomSerializer::StatePointer(const char* key, void* ptraddr, bool
 }
 
 
+FSerializer& Serialize(FSerializer& arc, const char* key, TMap<FName, DObject*>& value, TMap<FName, DObject*>* def)
+{
+	if (!arc.BeginObject(key))
+		return arc;
+
+	if (arc.isWriting())
+	{
+		TMap<FName, DObject*>::Iterator it = { value };
+		TMap<FName, DObject*>::Pair* pair = nullptr;
+		while (it.NextPair(pair))
+			arc(pair->Key.GetChars(), pair->Value);
+	}
+	else
+	{
+		const char* k = nullptr;
+		while ((k = arc.GetKey()) != nullptr)
+		{
+			DObject* obj = nullptr;
+			arc(k, obj);
+			value[k] = obj;
+		}
+	}
+
+	arc.EndObject();
+	return arc;
+}
+
 
 template<> FSerializer &Serialize(FSerializer &ar, const char *key, FPolyObj *&value, FPolyObj **defval)
 {
diff --git a/src/serializer_doom.h b/src/serializer_doom.h
index 40b6710a17..ec1a54fb89 100644
--- a/src/serializer_doom.h
+++ b/src/serializer_doom.h
@@ -43,6 +43,7 @@ FSerializer &Serialize(FSerializer &arc, const char *key, ticcmd_t &sid, ticcmd_
 FSerializer &Serialize(FSerializer &arc, const char *key, usercmd_t &cmd, usercmd_t *def);
 FSerializer &Serialize(FSerializer &arc, const char *key, FInterpolator &rs, FInterpolator *def);
 FSerializer& Serialize(FSerializer& arc, const char* key, struct FStandaloneAnimation& value, struct FStandaloneAnimation* defval);
+FSerializer& Serialize(FSerializer& arc, const char* key, TMap<FName, DObject*>& value, TMap<FName, DObject*>* def);
 
 template<> FSerializer &Serialize(FSerializer &arc, const char *key, FPolyObj *&value, FPolyObj **defval);
 template<> FSerializer &Serialize(FSerializer &arc, const char *key, sector_t *&value, sector_t **defval);
diff --git a/wadsrc/static/zscript/actors/actor.zs b/wadsrc/static/zscript/actors/actor.zs
index a809e674d9..7861258fe1 100644
--- a/wadsrc/static/zscript/actors/actor.zs
+++ b/wadsrc/static/zscript/actors/actor.zs
@@ -73,6 +73,14 @@ class ViewPosition native
 	native readonly int Flags;
 }
 
+class Behavior play abstract
+{
+	readonly Actor Owner;
+
+	virtual void Initialize() {}
+	virtual void Readded() {}
+	virtual void Tick() {}
+}
 
 class Actor : Thinker native
 {
@@ -500,6 +508,13 @@ class Actor : Thinker native
 		return sin(fb * (180./32)) * 8;
 	}
 
+	native clearscope Behavior FindBehavior(class<Behavior> type) const;
+	native bool RemoveBehavior(class<Behavior> type);
+	native Behavior AddBehavior(class<Behavior> type);
+	native void TickBehaviors();
+	native void ClearBehaviors();
+	native void MoveBehaviors(Actor from);
+
 	native clearscope bool isFrozen() const;
 	virtual native void BeginPlay();
 	virtual native void Activate(Actor activator);