diff --git a/src/g_game.cpp b/src/g_game.cpp
index 799a4e7aa..c97ea2198 100644
--- a/src/g_game.cpp
+++ b/src/g_game.cpp
@@ -1557,7 +1557,7 @@ void G_DeathMatchSpawnPlayer (int playernum)
 			if (spot == NULL)
 			{ // We have a player 1 start, right?
 				spot = &playerstarts[0];
-				if (spot == NULL)
+				if (spot->type == 0)
 				{ // Fine, whatever.
 					spot = &deathmatchstarts[0];
 				}
@@ -1573,7 +1573,8 @@ void G_DeathMatchSpawnPlayer (int playernum)
 //
 FPlayerStart *G_PickPlayerStart(int playernum, int flags)
 {
-	if ((level.flags2 & LEVEL2_RANDOMPLAYERSTARTS) || (flags & PPS_FORCERANDOM))
+	if ((level.flags2 & LEVEL2_RANDOMPLAYERSTARTS) || (flags & PPS_FORCERANDOM) ||
+		playerstarts[playernum].type == 0)
 	{
 		if (!(flags & PPS_NOBLOCKINGCHECK))
 		{
@@ -1592,7 +1593,7 @@ FPlayerStart *G_PickPlayerStart(int playernum, int flags)
 			{ // Pick an open spot at random.
 				return good_starts[pr_pspawn(good_starts.Size())];
 			}
-	}
+		}
 		// Pick a spot at random, whether it's open or not.
 		return &AllPlayerStarts[pr_pspawn(AllPlayerStarts.Size())];
 	}
@@ -1665,16 +1666,17 @@ void G_DoReborn (int playernum, bool freshbot)
 		}
 
 		if (!(level.flags2 & LEVEL2_RANDOMPLAYERSTARTS) &&
+			playerstarts[playernum].type != 0 &&
 			G_CheckSpot (playernum, &playerstarts[playernum]))
 		{
 			AActor *mo = P_SpawnPlayer(&playerstarts[playernum], playernum);
-			if (mo != NULL) P_PlayerStartStomp(mo);
+			if (mo != NULL) P_PlayerStartStomp(mo, true);
 		}
 		else
 		{ // try to spawn at any random player's spot
 			FPlayerStart *start = G_PickPlayerStart(playernum, PPS_FORCERANDOM);
 			AActor *mo = P_SpawnPlayer(start, playernum);
-			if (mo != NULL) P_PlayerStartStomp(mo);
+			if (mo != NULL) P_PlayerStartStomp(mo, true);
 		}
 	}
 }
diff --git a/src/g_heretic/a_hereticweaps.cpp b/src/g_heretic/a_hereticweaps.cpp
index ba216a8ba..899514139 100644
--- a/src/g_heretic/a_hereticweaps.cpp
+++ b/src/g_heretic/a_hereticweaps.cpp
@@ -505,23 +505,14 @@ DEFINE_ACTION_FUNCTION(AActor, A_MaceBallImpact2)
 	AActor *tiny;
 	angle_t angle;
 
+	if ((self->Z() <= self->floorz) && P_HitFloor (self))
+	{ // Landed in some sort of liquid
+		self->Destroy ();
+		return;
+	}
 	if (self->flags & MF_INBOUNCE)
 	{
-		fixed_t floordist = self->Z() - self->floorz;
-		fixed_t ceildist = self->ceilingz - self->Z();
-		fixed_t vel;
-
-		// NOTE: The assumptions being made here about the plane to use for bouncing off are dead wrong.
-		// http://forum.zdoom.org/viewtopic.php?f=2&t=50449
-		if (floordist <= ceildist)
-		{
-			vel = MulScale32 (self->velz, self->Sector->floorplane.c);
-		}
-		else
-		{
-			vel = MulScale32 (self->velz, self->Sector->ceilingplane.c);
-		}
-		if (vel < 2)
+		if (self->velz < 2*FRACUNIT)
 		{
 			goto boom;
 		}
@@ -619,21 +610,7 @@ DEFINE_ACTION_FUNCTION(AActor, A_DeathBallImpact)
 	}
 	if (self->flags & MF_INBOUNCE)
 	{
-		fixed_t floordist = self->Z() - self->floorz;
-		fixed_t ceildist = self->ceilingz - self->Z();
-		fixed_t vel;
-
-		// NOTE: The assumptions being made here about the plane to use for bouncing off are dead wrong.
-		// http://forum.zdoom.org/viewtopic.php?f=2&t=50449
-		if (floordist <= ceildist)
-		{
-			vel = MulScale32 (self->velz, self->Sector->floorplane.c);
-		}
-		else
-		{
-			vel = MulScale32 (self->velz, self->Sector->ceilingplane.c);
-		}
-		if (vel < 2)
+		if (self->velz < 2*FRACUNIT)
 		{
 			goto boom;
 		}
diff --git a/src/m_cheat.cpp b/src/m_cheat.cpp
index 3bab8f7e5..b6316f732 100644
--- a/src/m_cheat.cpp
+++ b/src/m_cheat.cpp
@@ -136,6 +136,7 @@ void cht_DoCheat (player_t *player, int cheat)
 			player->cheats &= ~CF_NOCLIP;
 			msg = GStrings("STSTR_NCOFF");
 		}
+		player->mo->velx = 1;	// force some lateral movement so that internal variables are up to date
 		break;
 
 	case CHT_NOVELOCITY:
diff --git a/src/p_3dfloors.cpp b/src/p_3dfloors.cpp
index 6f507d9a1..f915c3e0f 100644
--- a/src/p_3dfloors.cpp
+++ b/src/p_3dfloors.cpp
@@ -293,6 +293,7 @@ static int P_Set3DFloor(line_t * line, int param, int param2, int alpha)
 			// if flooding is used the floor must be non-solid and is automatically made shootthrough and seethrough
 			if ((param2 & 128) && !(flags & FF_SOLID)) flags |= FF_FLOOD | FF_SEETHROUGH | FF_SHOOTTHROUGH;
 			if (param2 & 512) flags |= FF_FADEWALLS;
+			if (param2&1024) flags |= FF_RESET;
 			FTextureID tex = line->sidedef[0]->GetTexture(side_t::top);
 			if (!tex.Exists() && alpha < 255)
 			{
@@ -437,6 +438,7 @@ void P_Recalculate3DFloors(sector_t * sector)
 	fixed_t			maxheight, minheight;
 	unsigned		i, j;
 	lightlist_t newlight;
+	lightlist_t resetlight;	// what it goes back to after FF_DOUBLESHADOW
 
 	TArray<F3DFloor*> & ffloors=sector->e->XFloor.ffloors;
 	TArray<lightlist_t> & lightlist = sector->e->XFloor.lightlist;
@@ -593,6 +595,9 @@ void P_Recalculate3DFloors(sector_t * sector)
 		lightlist[0].flags = 0;
 		lightlist[0].fromsector = true;
 		
+
+		resetlight = lightlist[0];
+
 		maxheight = sector->CenterCeiling();
 		minheight = sector->CenterFloor();
 		for(i = 0; i < ffloors.Size(); i++)
@@ -616,7 +621,7 @@ void P_Recalculate3DFloors(sector_t * sector)
 				newlight.fromsector = false;
 				lightlist.Push(newlight);
 			}
-			else if (i==0)
+			else
 			{
 				fixed_t ff_bottom=rover->bottom.plane->ZatPoint(CenterSpot(sector));
 				if (ff_bottom<maxheight)
@@ -631,6 +636,18 @@ void P_Recalculate3DFloors(sector_t * sector)
 					lightlist[0].fromsector = false;
 				}
 			}
+			if (!(rover->flags & (FF_DOUBLESHADOW | FF_RESET)))
+			{
+				resetlight = lightlist.Last();
+			}
+			else if (rover->flags & FF_RESET)
+			{
+				resetlight.p_lightlevel = &sector->lightlevel;
+				resetlight.lightsource = NULL;
+				resetlight.extra_colormap = sector->ColorMap;
+				resetlight.blend = 0;
+			}
+
 			if (rover->flags&FF_DOUBLESHADOW)
 			{
 				fixed_t ff_bottom=rover->bottom.plane->ZatPoint(CenterSpot(sector));
@@ -638,20 +655,10 @@ void P_Recalculate3DFloors(sector_t * sector)
 				{
 					newlight.caster = rover;
 					newlight.plane = *rover->bottom.plane;
-					if (lightlist.Size()>1)
-					{
-						newlight.lightsource = lightlist[lightlist.Size()-2].lightsource;
-						newlight.p_lightlevel = lightlist[lightlist.Size()-2].p_lightlevel;
-						newlight.extra_colormap = lightlist[lightlist.Size()-2].extra_colormap;
-						newlight.blend = lightlist[lightlist.Size()-2].blend;
-					}
-					else
-					{
-						newlight.lightsource = NULL;
-						newlight.p_lightlevel = &sector->lightlevel;
-						newlight.extra_colormap = sector->ColorMap;
-						newlight.blend = 0;
-					}
+					newlight.lightsource = resetlight.lightsource;
+					newlight.p_lightlevel = resetlight.p_lightlevel;
+					newlight.extra_colormap = resetlight.extra_colormap;
+					newlight.blend = resetlight.blend;
 					newlight.flags = rover->flags;
 					newlight.fromsector = false;
 					lightlist.Push(newlight);
@@ -832,7 +839,7 @@ void P_LineOpening_XFloors (FLineOpening &open, AActor * thing, const line_t *li
 //==========================================================================
 void P_Spawn3DFloors (void)
 {
-	static int flagvals[] = {128+512, 2+512, 512};
+	static int flagvals[] = {512, 2+512, 512+1024};
 	int i;
 	line_t * line;
 
diff --git a/src/p_3dfloors.h b/src/p_3dfloors.h
index 1dad6d9e5..93fd13d1b 100644
--- a/src/p_3dfloors.h
+++ b/src/p_3dfloors.h
@@ -35,6 +35,7 @@ typedef enum
   FF_ADDITIVETRANS	   = 0x10000000, // Render this floor with additive translucency
   FF_FLOOD			   = 0x20000000, // extends towards the next lowest flooding or solid 3D floor or the bottom of the sector
   FF_THISINSIDE		   = 0x40000000, // hack for software 3D with FF_BOTHPLANES
+  FF_RESET			   = 0x80000000, // light effect is completely reset, once interrupted  
 } ffloortype_e;
 
 // This is for the purpose of Sector_SetContents:
diff --git a/src/p_acs.cpp b/src/p_acs.cpp
index 3aab261f4..9737f8aa9 100644
--- a/src/p_acs.cpp
+++ b/src/p_acs.cpp
@@ -217,6 +217,49 @@ FWorldGlobalArray ACS_WorldArrays[NUM_WORLDVARS];
 SDWORD ACS_GlobalVars[NUM_GLOBALVARS];
 FWorldGlobalArray ACS_GlobalArrays[NUM_GLOBALVARS];
 
+//----------------------------------------------------------------------------
+//
+// ACS stack manager
+//
+// This is needed so that the garbage collector has access to all active
+// script stacks
+//
+//----------------------------------------------------------------------------
+
+struct FACSStack
+{
+	SDWORD buffer[STACK_SIZE];
+	int sp;
+	FACSStack *next;
+	FACSStack *prev;
+	static FACSStack *head;
+
+	FACSStack();
+	~FACSStack();
+};
+
+FACSStack *FACSStack::head;
+
+FACSStack::FACSStack()
+{
+	sp = 0;
+	next = head;
+	prev = NULL;
+	head = this;
+}
+
+FACSStack::~FACSStack()
+{
+	if (next != NULL) next->prev = prev;
+	if (prev == NULL)
+	{
+		head = next;
+	}
+	else
+	{
+		prev->next = next;
+	}
+}
 
 //----------------------------------------------------------------------------
 //
@@ -290,7 +333,7 @@ void ACSStringPool::Clear()
 //
 //============================================================================
 
-int ACSStringPool::AddString(const char *str, const SDWORD *stack, int stackdepth)
+int ACSStringPool::AddString(const char *str)
 {
 	size_t len = strlen(str);
 	unsigned int h = SuperFastHash(str, len);
@@ -301,10 +344,10 @@ int ACSStringPool::AddString(const char *str, const SDWORD *stack, int stackdept
 		return i | STRPOOL_LIBRARYID_OR;
 	}
 	FString fstr(str);
-	return InsertString(fstr, h, bucketnum, stack, stackdepth);
+	return InsertString(fstr, h, bucketnum);
 }
 
-int ACSStringPool::AddString(FString &str, const SDWORD *stack, int stackdepth)
+int ACSStringPool::AddString(FString &str)
 {
 	unsigned int h = SuperFastHash(str.GetChars(), str.Len());
 	unsigned int bucketnum = h % NUM_BUCKETS;
@@ -313,7 +356,7 @@ int ACSStringPool::AddString(FString &str, const SDWORD *stack, int stackdepth)
 	{
 		return i | STRPOOL_LIBRARYID_OR;
 	}
-	return InsertString(str, h, bucketnum, stack, stackdepth);
+	return InsertString(str, h, bucketnum);
 }
 
 //============================================================================
@@ -583,12 +626,12 @@ int ACSStringPool::FindString(const char *str, size_t len, unsigned int h, unsig
 //
 //============================================================================
 
-int ACSStringPool::InsertString(FString &str, unsigned int h, unsigned int bucketnum, const SDWORD *stack, int stackdepth)
+int ACSStringPool::InsertString(FString &str, unsigned int h, unsigned int bucketnum)
 {
 	unsigned int index = FirstFreeEntry;
 	if (index >= MIN_GC_SIZE && index == Pool.Max())
 	{ // We will need to grow the array. Try a garbage collection first.
-		P_CollectACSGlobalStrings(stack, stackdepth);
+		P_CollectACSGlobalStrings();
 		index = FirstFreeEntry;
 	}
 	if (FirstFreeEntry >= STRPOOL_LIBRARYID_OR)
@@ -772,11 +815,11 @@ void P_MarkGlobalVarStrings()
 //
 //============================================================================
 
-void P_CollectACSGlobalStrings(const SDWORD *stack, int stackdepth)
+void P_CollectACSGlobalStrings()
 {
-	if (stack != NULL && stackdepth != 0)
+	for (FACSStack *stack = FACSStack::head; stack != NULL; stack = stack->next)
 	{
-		GlobalACSStrings.MarkStringArray(stack, stackdepth);
+		GlobalACSStrings.MarkStringArray(stack->buffer, stack->sp);
 	}
 	FBehavior::StaticMarkLevelVarStrings();
 	P_MarkWorldVarStrings();
@@ -787,7 +830,7 @@ void P_CollectACSGlobalStrings(const SDWORD *stack, int stackdepth)
 #ifdef _DEBUG
 CCMD(acsgc)
 {
-	P_CollectACSGlobalStrings(NULL, 0);
+	P_CollectACSGlobalStrings();
 }
 CCMD(globstr)
 {
@@ -1995,7 +2038,7 @@ bool FBehavior::Init(int lumpnum, FileReader * fr, int len)
 					const char *str = LookupString(MapVarStore[LittleLong(chunk[i+2])]);
 					if (str != NULL)
 					{
-						MapVarStore[LittleLong(chunk[i+2])] = GlobalACSStrings.AddString(str, NULL, 0);
+						MapVarStore[LittleLong(chunk[i+2])] = GlobalACSStrings.AddString(str);
 					}
 				}
 			}
@@ -2015,7 +2058,7 @@ bool FBehavior::Init(int lumpnum, FileReader * fr, int len)
 							const char *str = LookupString(*elems);
 							if (str != NULL)
 							{
-								*elems = GlobalACSStrings.AddString(str, NULL, 0);
+								*elems = GlobalACSStrings.AddString(str);
 							}
 						}
 					}
@@ -2049,7 +2092,7 @@ bool FBehavior::Init(int lumpnum, FileReader * fr, int len)
 								const char *str = LookupString(*elems);
 								if (str != NULL)
 								{
-									*elems = GlobalACSStrings.AddString(str, NULL, 0);
+									*elems = GlobalACSStrings.AddString(str);
 								}
 							}
 						}
@@ -3949,7 +3992,7 @@ void DLevelScript::DoSetActorProperty (AActor *actor, int property, int value)
 	}
 }
 
-int DLevelScript::GetActorProperty (int tid, int property, const SDWORD *stack, int stackdepth)
+int DLevelScript::GetActorProperty (int tid, int property)
 {
 	AActor *actor = SingleActorFromTID (tid, activator);
 
@@ -4034,13 +4077,13 @@ int DLevelScript::GetActorProperty (int tid, int property, const SDWORD *stack,
 								return 0;
 							}
 
-	case APROP_SeeSound:	return GlobalACSStrings.AddString(actor->SeeSound, stack, stackdepth);
-	case APROP_AttackSound:	return GlobalACSStrings.AddString(actor->AttackSound, stack, stackdepth);
-	case APROP_PainSound:	return GlobalACSStrings.AddString(actor->PainSound, stack, stackdepth);
-	case APROP_DeathSound:	return GlobalACSStrings.AddString(actor->DeathSound, stack, stackdepth);
-	case APROP_ActiveSound:	return GlobalACSStrings.AddString(actor->ActiveSound, stack, stackdepth);
-	case APROP_Species:		return GlobalACSStrings.AddString(actor->GetSpecies(), stack, stackdepth);
-	case APROP_NameTag:		return GlobalACSStrings.AddString(actor->GetTag(), stack, stackdepth);
+	case APROP_SeeSound:	return GlobalACSStrings.AddString(actor->SeeSound);
+	case APROP_AttackSound:	return GlobalACSStrings.AddString(actor->AttackSound);
+	case APROP_PainSound:	return GlobalACSStrings.AddString(actor->PainSound);
+	case APROP_DeathSound:	return GlobalACSStrings.AddString(actor->DeathSound);
+	case APROP_ActiveSound:	return GlobalACSStrings.AddString(actor->ActiveSound);
+	case APROP_Species:		return GlobalACSStrings.AddString(actor->GetSpecies());
+	case APROP_NameTag:		return GlobalACSStrings.AddString(actor->GetTag());
 	case APROP_StencilColor:return actor->fillcolor;
 	case APROP_Friction:	return actor->Friction;
 
@@ -4090,7 +4133,7 @@ int DLevelScript::CheckActorProperty (int tid, int property, int value)
 		case APROP_ViewHeight:
 		case APROP_AttackZOffset:
 		case APROP_StencilColor:
-			return (GetActorProperty(tid, property, NULL, 0) == value);
+			return (GetActorProperty(tid, property) == value);
 
 		// Boolean values need to compare to a binary version of value
 		case APROP_Ambush:
@@ -4102,7 +4145,7 @@ int DLevelScript::CheckActorProperty (int tid, int property, int value)
 		case APROP_Notarget:
 		case APROP_Notrigger:
 		case APROP_Dormant:
-			return (GetActorProperty(tid, property, NULL, 0) == (!!value));
+			return (GetActorProperty(tid, property) == (!!value));
 
 		// Strings are covered by GetActorProperty, but they're fairly
 		// heavy-duty, so make the check here.
@@ -4614,14 +4657,14 @@ static void DoSetCVar(FBaseCVar *cvar, int value, bool is_string, bool force=fal
 }
 
 // Converts floating- to fixed-point as required.
-static int DoGetCVar(FBaseCVar *cvar, bool is_string, const SDWORD *stack, int stackdepth)
+static int DoGetCVar(FBaseCVar *cvar, bool is_string)
 {
 	UCVarValue val;
 
 	if (is_string)
 	{
 		val = cvar->GetGenericRep(CVAR_String);
-		return GlobalACSStrings.AddString(val.String, stack, stackdepth);
+		return GlobalACSStrings.AddString(val.String);
 	}
 	else if (cvar->GetRealType() == CVAR_Float)
 	{
@@ -4635,7 +4678,7 @@ static int DoGetCVar(FBaseCVar *cvar, bool is_string, const SDWORD *stack, int s
 	}
 }
 
-static int GetUserCVar(int playernum, const char *cvarname, bool is_string, const SDWORD *stack, int stackdepth)
+static int GetUserCVar(int playernum, const char *cvarname, bool is_string)
 {
 	if ((unsigned)playernum >= MAXPLAYERS || !playeringame[playernum])
 	{
@@ -4647,10 +4690,10 @@ static int GetUserCVar(int playernum, const char *cvarname, bool is_string, cons
 	{
 		return 0;
 	}
-	return DoGetCVar(cvar, is_string, stack, stackdepth);
+	return DoGetCVar(cvar, is_string);
 }
 
-static int GetCVar(AActor *activator, const char *cvarname, bool is_string, const SDWORD *stack, int stackdepth)
+static int GetCVar(AActor *activator, const char *cvarname, bool is_string)
 {
 	FBaseCVar *cvar = FindCVar(cvarname, NULL);
 	// Either the cvar doesn't exist, or it's for a mod that isn't loaded, so return 0.
@@ -4667,9 +4710,9 @@ static int GetCVar(AActor *activator, const char *cvarname, bool is_string, cons
 			{
 				return 0;
 			}
-			return GetUserCVar(int(activator->player - players), cvarname, is_string, stack, stackdepth);
+			return GetUserCVar(int(activator->player - players), cvarname, is_string);
 		}
-		return DoGetCVar(cvar, is_string, stack, stackdepth);
+		return DoGetCVar(cvar, is_string);
 	}
 }
 
@@ -4860,7 +4903,7 @@ static int SwapActorTeleFog(AActor *activator, int tid)
 
 
 
-int DLevelScript::CallFunction(int argCount, int funcIndex, SDWORD *args, const SDWORD *stack, int stackdepth)
+int DLevelScript::CallFunction(int argCount, int funcIndex, SDWORD *args)
 {
 	AActor *actor;
 	switch(funcIndex)
@@ -5031,7 +5074,7 @@ int DLevelScript::CallFunction(int argCount, int funcIndex, SDWORD *args, const
 				switch(args[0])
 				{
 					case ARMORINFO_CLASSNAME:
-						return GlobalACSStrings.AddString(equippedarmor->ArmorType.GetChars(), stack, stackdepth);
+						return GlobalACSStrings.AddString(equippedarmor->ArmorType.GetChars());
 
 					case ARMORINFO_SAVEAMOUNT:
 						return equippedarmor->MaxAmount;
@@ -5052,7 +5095,7 @@ int DLevelScript::CallFunction(int argCount, int funcIndex, SDWORD *args, const
 						return 0;
 				}
 			}
-			return args[0] == ARMORINFO_CLASSNAME ? GlobalACSStrings.AddString("None", stack, stackdepth) : 0;
+			return args[0] == ARMORINFO_CLASSNAME ? GlobalACSStrings.AddString("None") : 0;
 		}
 
 		case ACSF_SpawnSpotForced:
@@ -5171,7 +5214,7 @@ int DLevelScript::CallFunction(int argCount, int funcIndex, SDWORD *args, const
 		case ACSF_GetActorClass:
 		{
 			AActor *a = SingleActorFromTID(args[0], activator);
-			return GlobalACSStrings.AddString(a == NULL ? "None" : a->GetClass()->TypeName.GetChars(), stack, stackdepth);
+			return GlobalACSStrings.AddString(a == NULL ? "None" : a->GetClass()->TypeName.GetChars());
 		}
 
 		case ACSF_SoundSequenceOnActor:
@@ -5349,7 +5392,7 @@ int DLevelScript::CallFunction(int argCount, int funcIndex, SDWORD *args, const
 		case ACSF_GetCVarString:
 			if (argCount == 1)
 			{
-				return GetCVar(activator, FBehavior::StaticLookupString(args[0]), true, stack, stackdepth);
+				return GetCVar(activator, FBehavior::StaticLookupString(args[0]), true);
 			}
 			break;
 
@@ -5370,14 +5413,14 @@ int DLevelScript::CallFunction(int argCount, int funcIndex, SDWORD *args, const
 		case ACSF_GetUserCVar:
 			if (argCount == 2)
 			{
-				return GetUserCVar(args[0], FBehavior::StaticLookupString(args[1]), false, stack, stackdepth);
+				return GetUserCVar(args[0], FBehavior::StaticLookupString(args[1]), false);
 			}
 			break;
 
 		case ACSF_GetUserCVarString:
 			if (argCount == 2)
 			{
-				return GetUserCVar(args[0], FBehavior::StaticLookupString(args[1]), true, stack, stackdepth);
+				return GetUserCVar(args[0], FBehavior::StaticLookupString(args[1]), true);
 			}
 			break;
 
@@ -5564,7 +5607,7 @@ doplaysound:			if (funcIndex == ACSF_PlayActorSound)
 				const char *oldstr = FBehavior::StaticLookupString(args[0]);
 				if (oldstr == NULL || *oldstr == '\0')
 				{
-					return GlobalACSStrings.AddString("", stack, stackdepth);
+					return GlobalACSStrings.AddString("");
 				}
 				size_t oldlen = strlen(oldstr);
 				size_t newlen = args[1];
@@ -5574,7 +5617,7 @@ doplaysound:			if (funcIndex == ACSF_PlayActorSound)
 					newlen = oldlen;
 				}
 				FString newstr(funcIndex == ACSF_StrLeft ? oldstr : oldstr + oldlen - newlen, newlen);
-				return GlobalACSStrings.AddString(newstr, stack, stackdepth);
+				return GlobalACSStrings.AddString(newstr);
 			}
 			break;
 
@@ -5584,7 +5627,7 @@ doplaysound:			if (funcIndex == ACSF_PlayActorSound)
 				const char *oldstr = FBehavior::StaticLookupString(args[0]);
 				if (oldstr == NULL || *oldstr == '\0')
 				{
-					return GlobalACSStrings.AddString("", stack, stackdepth);
+					return GlobalACSStrings.AddString("");
 				}
 				size_t oldlen = strlen(oldstr);
 				size_t pos = args[1];
@@ -5592,13 +5635,13 @@ doplaysound:			if (funcIndex == ACSF_PlayActorSound)
 
 				if (pos >= oldlen)
 				{
-					return GlobalACSStrings.AddString("", stack, stackdepth);
+					return GlobalACSStrings.AddString("");
 				}
 				if (pos + newlen > oldlen || pos + newlen < pos)
 				{
 					newlen = oldlen - pos;
 				}
-				return GlobalACSStrings.AddString(FString(oldstr + pos, newlen), stack, stackdepth);
+				return GlobalACSStrings.AddString(FString(oldstr + pos, newlen));
 			}
 			break;
 
@@ -5606,11 +5649,11 @@ doplaysound:			if (funcIndex == ACSF_PlayActorSound)
             if (activator == NULL || activator->player == NULL || // Non-players do not have weapons
                 activator->player->ReadyWeapon == NULL)
             {
-                return GlobalACSStrings.AddString("None", stack, stackdepth);
+                return GlobalACSStrings.AddString("None");
             }
             else
             {
-				return GlobalACSStrings.AddString(activator->player->ReadyWeapon->GetClass()->TypeName.GetChars(), stack, stackdepth);
+				return GlobalACSStrings.AddString(activator->player->ReadyWeapon->GetClass()->TypeName.GetChars());
             }
 
 		case ACSF_SpawnDecal:
@@ -6157,8 +6200,10 @@ int DLevelScript::RunScript ()
 		break;
 	}
 
-	SDWORD Stack[STACK_SIZE];
-	int sp = 0;
+	FACSStack stackobj;
+	SDWORD *Stack = stackobj.buffer;
+	int &sp = stackobj.sp;
+
 	int *pc = this->pc;
 	ACSFormat fmt = activeBehavior->GetFormat();
 	FBehavior* const savedActiveBehavior = activeBehavior;
@@ -6211,7 +6256,7 @@ int DLevelScript::RunScript ()
 
 		case PCD_TAGSTRING:
 			//Stack[sp-1] |= activeBehavior->GetLibraryID();
-			Stack[sp-1] = GlobalACSStrings.AddString(activeBehavior->LookupString(Stack[sp-1]), Stack, sp);
+			Stack[sp-1] = GlobalACSStrings.AddString(activeBehavior->LookupString(Stack[sp-1]));
 			break;
 
 		case PCD_PUSHNUMBER:
@@ -6409,7 +6454,7 @@ int DLevelScript::RunScript ()
 				int argCount = NEXTBYTE;
 				int funcIndex = NEXTSHORT;
 
-				int retval = CallFunction(argCount, funcIndex, &STACK(argCount), Stack, sp);
+				int retval = CallFunction(argCount, funcIndex, &STACK(argCount));
 				sp -= argCount-1;
 				STACK(1) = retval;
 			}
@@ -8933,7 +8978,7 @@ scriptwait:
 			break;
 
 		case PCD_GETACTORPROPERTY:
-			STACK(2) = GetActorProperty (STACK(2), STACK(1), Stack, sp);
+			STACK(2) = GetActorProperty (STACK(2), STACK(1));
 			sp -= 1;
 			break;
 
@@ -9030,7 +9075,7 @@ scriptwait:
 			break;
 
 		case PCD_GETCVAR:
-			STACK(1) = GetCVar(activator, FBehavior::StaticLookupString(STACK(1)), false, Stack, sp);
+			STACK(1) = GetCVar(activator, FBehavior::StaticLookupString(STACK(1)), false);
 			break;
 
 		case PCD_SETHUDSIZE:
@@ -9384,7 +9429,7 @@ scriptwait:
 		case PCD_SAVESTRING:
 			// Saves the string
 			{
-				const int str = GlobalACSStrings.AddString(work, Stack, sp);
+				const int str = GlobalACSStrings.AddString(work);
 				PushToStack(str);
 				STRINGBUILDER_FINISH(work);
 			}		
diff --git a/src/p_acs.h b/src/p_acs.h
index 3188e46aa..858364e2f 100644
--- a/src/p_acs.h
+++ b/src/p_acs.h
@@ -80,8 +80,8 @@ class ACSStringPool
 {
 public:
 	ACSStringPool();
-	int AddString(const char *str, const SDWORD *stack, int stackdepth);
-	int AddString(FString &str, const SDWORD *stack, int stackdepth);
+	int AddString(const char *str);
+	int AddString(FString &str);
 	const char *GetString(int strnum);
 	void LockString(int strnum);
 	void UnlockString(int strnum);
@@ -99,7 +99,7 @@ public:
 
 private:
 	int FindString(const char *str, size_t len, unsigned int h, unsigned int bucketnum);
-	int InsertString(FString &str, unsigned int h, unsigned int bucketnum, const SDWORD *stack, int stackdepth);
+	int InsertString(FString &str, unsigned int h, unsigned int bucketnum);
 	void FindFirstFreeEntry(unsigned int base);
 
 	enum { NUM_BUCKETS = 251 };
@@ -119,7 +119,7 @@ private:
 };
 extern ACSStringPool GlobalACSStrings;
 
-void P_CollectACSGlobalStrings(const SDWORD *stack, int stackdepth);
+void P_CollectACSGlobalStrings();
 void P_ReadACSVars(PNGHandle *);
 void P_WriteACSVars(FILE*);
 void P_ClearACSVars(bool);
@@ -910,7 +910,7 @@ protected:
 	int DoSpawnSpot (int type, int spot, int tid, int angle, bool forced);
 	int DoSpawnSpotFacing (int type, int spot, int tid, bool forced);
 	int DoClassifyActor (int tid);
-	int CallFunction(int argCount, int funcIndex, SDWORD *args, const SDWORD *stack, int stackdepth);
+	int CallFunction(int argCount, int funcIndex, SDWORD *args);
 
 	void DoFadeTo (int r, int g, int b, int a, fixed_t time);
 	void DoFadeRange (int r1, int g1, int b1, int a1,
@@ -918,7 +918,7 @@ protected:
 	void DoSetFont (int fontnum);
 	void SetActorProperty (int tid, int property, int value);
 	void DoSetActorProperty (AActor *actor, int property, int value);
-	int GetActorProperty (int tid, int property, const SDWORD *stack, int stackdepth);
+	int GetActorProperty (int tid, int property);
 	int CheckActorProperty (int tid, int property, int value);
 	int GetPlayerInput (int playernum, int inputnum);
 
diff --git a/src/p_enemy.cpp b/src/p_enemy.cpp
index 0fd23f73e..fa2804593 100644
--- a/src/p_enemy.cpp
+++ b/src/p_enemy.cpp
@@ -2724,9 +2724,9 @@ enum FAF_Flags
 	FAF_BOTTOM = 1,
 	FAF_MIDDLE = 2,
 	FAF_TOP = 4,
-	FAF_NODISTFACTOR = 8,
+	FAF_NODISTFACTOR = 8,	// deprecated
 };
-void A_Face (AActor *self, AActor *other, angle_t max_turn, angle_t max_pitch, angle_t ang_offset, angle_t pitch_offset, int flags)
+void A_Face (AActor *self, AActor *other, angle_t max_turn, angle_t max_pitch, angle_t ang_offset, angle_t pitch_offset, int flags, fixed_t z_add)
 {
 	if (!other)
 		return;
@@ -2799,8 +2799,8 @@ void A_Face (AActor *self, AActor *other, angle_t max_turn, angle_t max_pitch, a
 			target_z = other->Z() + (other->height / 2) + other->GetBobOffset();
 		if (flags & FAF_TOP)
 			target_z = other->Z() + (other->height) + other->GetBobOffset();
-		if (!(flags & FAF_NODISTFACTOR))
-			target_z += pitch_offset;
+
+		target_z += z_add;
 
 		double dist_z = target_z - source_z;
 		double ddist = sqrt(dist.X*dist.X + dist.Y*dist.Y + dist_z*dist_z);
@@ -2836,55 +2836,48 @@ void A_Face (AActor *self, AActor *other, angle_t max_turn, angle_t max_pitch, a
     }
 }
 
-void A_FaceTarget(AActor *self, angle_t max_turn, angle_t max_pitch, angle_t ang_offset, angle_t pitch_offset, int flags)
+void A_FaceTarget(AActor *self)
 {
-	A_Face(self, self->target, max_turn, max_pitch, ang_offset, pitch_offset, flags);
-}
-
-void A_FaceMaster(AActor *self, angle_t max_turn, angle_t max_pitch, angle_t ang_offset, angle_t pitch_offset, int flags)
-{
-	A_Face(self, self->master, max_turn, max_pitch, ang_offset, pitch_offset, flags);
-}
-
-void A_FaceTracer(AActor *self, angle_t max_turn, angle_t max_pitch, angle_t ang_offset, angle_t pitch_offset, int flags)
-{
-	A_Face(self, self->tracer, max_turn, max_pitch, ang_offset, pitch_offset, flags);
+	A_Face(self, self->target);
 }
 
 DEFINE_ACTION_FUNCTION_PARAMS(AActor, A_FaceTarget)
 {
-	ACTION_PARAM_START(5);
+	ACTION_PARAM_START(6);
 	ACTION_PARAM_ANGLE(max_turn, 0);
 	ACTION_PARAM_ANGLE(max_pitch, 1);
 	ACTION_PARAM_ANGLE(ang_offset, 2);
 	ACTION_PARAM_ANGLE(pitch_offset, 3);
 	ACTION_PARAM_INT(flags, 4);
+	ACTION_PARAM_FIXED(z_add, 5);
 
-	A_FaceTarget(self, max_turn, max_pitch, ang_offset, pitch_offset, flags);
+	A_Face(self, self->target, max_turn, max_pitch, ang_offset, pitch_offset, flags, z_add);
 }
 
 DEFINE_ACTION_FUNCTION_PARAMS(AActor, A_FaceMaster)
 {
-	ACTION_PARAM_START(5);
+	ACTION_PARAM_START(6);
 	ACTION_PARAM_ANGLE(max_turn, 0);
 	ACTION_PARAM_ANGLE(max_pitch, 1);
 	ACTION_PARAM_ANGLE(ang_offset, 2);
 	ACTION_PARAM_ANGLE(pitch_offset, 3);
 	ACTION_PARAM_INT(flags, 4);
+	ACTION_PARAM_FIXED(z_add, 5);
 
-	A_FaceMaster(self, max_turn, max_pitch, ang_offset, pitch_offset, flags);
+	A_Face(self, self->master, max_turn, max_pitch, ang_offset, pitch_offset, flags, z_add);
 }
 
 DEFINE_ACTION_FUNCTION_PARAMS(AActor, A_FaceTracer)
 {
-	ACTION_PARAM_START(5);
+	ACTION_PARAM_START(6);
 	ACTION_PARAM_ANGLE(max_turn, 0);
 	ACTION_PARAM_ANGLE(max_pitch, 1);
 	ACTION_PARAM_ANGLE(ang_offset, 2);
 	ACTION_PARAM_ANGLE(pitch_offset, 3);
 	ACTION_PARAM_INT(flags, 4);
+	ACTION_PARAM_FIXED(z_add, 5);
 
-	A_FaceTracer(self, max_turn, max_pitch, ang_offset, pitch_offset, flags);
+	A_Face(self, self->tracer, max_turn, max_pitch, ang_offset, pitch_offset, flags, z_add);
 }
 
 //===========================================================================
diff --git a/src/p_enemy.h b/src/p_enemy.h
index 799b4c0ff..9ee77caed 100644
--- a/src/p_enemy.h
+++ b/src/p_enemy.h
@@ -72,8 +72,8 @@ DECLARE_ACTION(A_FreezeDeathChunks)
 DECLARE_ACTION(A_BossDeath)
 
 void A_Chase(AActor *self);
-void A_FaceTarget(AActor *actor, angle_t max_turn = 0, angle_t max_pitch = ANGLE_270, angle_t ang_offset = 0, angle_t pitch_offset = 0, int flags = 0);
-void A_Face(AActor *self, AActor *other, angle_t max_turn = 0, angle_t max_pitch = ANGLE_270, angle_t ang_offset = 0, angle_t pitch_offset = 0, int flags = 0);
+void A_FaceTarget(AActor *actor);
+void A_Face(AActor *self, AActor *other, angle_t max_turn = 0, angle_t max_pitch = ANGLE_270, angle_t ang_offset = 0, angle_t pitch_offset = 0, int flags = 0, fixed_t pitch_add = 0);
 
 bool A_RaiseMobj (AActor *, fixed_t speed);
 bool A_SinkMobj (AActor *, fixed_t speed);
diff --git a/src/p_local.h b/src/p_local.h
index 420fff565..c39bcef78 100644
--- a/src/p_local.h
+++ b/src/p_local.h
@@ -485,7 +485,7 @@ inline bool	P_TeleportMove(AActor* thing, const fixedvec3 &pos, bool telefrag, b
 {
 	return P_TeleportMove(thing, pos.x, pos.y, pos.z, telefrag, modifyactor);
 }
-void	P_PlayerStartStomp (AActor *actor);		// [RH] Stomp on things for a newly spawned player
+void	P_PlayerStartStomp (AActor *actor, bool mononly=false);		// [RH] Stomp on things for a newly spawned player
 void	P_SlideMove (AActor* mo, fixed_t tryx, fixed_t tryy, int numsteps);
 bool	P_BounceWall (AActor *mo);
 bool	P_BounceActor (AActor *mo, AActor *BlockingMobj, bool ontop);
diff --git a/src/p_map.cpp b/src/p_map.cpp
index d096beb0d..1aacff982 100644
--- a/src/p_map.cpp
+++ b/src/p_map.cpp
@@ -430,6 +430,12 @@ bool P_TeleportMove(AActor *thing, fixed_t x, fixed_t y, fixed_t z, bool telefra
 		if (abs(th->X() - tmf.x) >= blockdist || abs(th->Y() - tmf.y) >= blockdist)
 			continue;
 
+		if ((th->flags2 | tmf.thing->flags2) & MF2_THRUACTORS)
+			continue;
+
+		if (tmf.thing->flags6 & MF6_THRUSPECIES && tmf.thing->GetSpecies() == th->GetSpecies())
+			continue;
+
 		// [RH] Z-Check
 		// But not if not MF2_PASSMOBJ or MF3_DONTOVERLAP are set!
 		// Otherwise those things would get stuck inside each other.
@@ -504,7 +510,7 @@ bool P_TeleportMove(AActor *thing, fixed_t x, fixed_t y, fixed_t z, bool telefra
 //
 //==========================================================================
 
-void P_PlayerStartStomp(AActor *actor)
+void P_PlayerStartStomp(AActor *actor, bool mononly)
 {
 	AActor *th;
 	FBlockThingsIterator it(FBoundingBox(actor->X(), actor->Y(), actor->radius));
@@ -525,6 +531,9 @@ void P_PlayerStartStomp(AActor *actor)
 		if (th->player == NULL && !(th->flags3 & MF3_ISMONSTER))
 			continue;
 
+		if (th->player != NULL && mononly)
+			continue;
+
 		if (actor->Z() > th->Top())
 			continue;        // overhead
 		if (actor->Top() < th->Z())
diff --git a/src/p_mobj.cpp b/src/p_mobj.cpp
index 67f7d1685..c9693ba47 100644
--- a/src/p_mobj.cpp
+++ b/src/p_mobj.cpp
@@ -4084,7 +4084,7 @@ AActor *AActor::StaticSpawn (const PClass *type, fixed_t ix, fixed_t iy, fixed_t
 	}
 	else
 	{
-		actor->SpawnPoint[2] = (actor->Z() - actor->floorz);
+		actor->SpawnPoint[2] = (actor->Z() - actor->Sector->floorplane.ZatPoint(actor));
 	}
 
 	if (actor->FloatBobPhase == (BYTE)-1) actor->FloatBobPhase = rng();	// Don't make everything bob in sync (unless deliberately told to do)
diff --git a/src/p_saveg.cpp b/src/p_saveg.cpp
index d0aa237b8..8683ea8e6 100644
--- a/src/p_saveg.cpp
+++ b/src/p_saveg.cpp
@@ -425,7 +425,6 @@ void P_SerializeWorld (FArchive &arc)
 			short secretsector;
 			arc << secretsector;
 			if (secretsector) sec->Flags |= SECF_WASSECRET;
-			sec->special &= ~(SECRET_MASK|FRICTION_MASK|PUSH_MASK);
 			P_InitSectorSpecial(sec, sec->special, true);
 		}
 		arc	<< sec->interpolations[0]
diff --git a/src/p_sectors.cpp b/src/p_sectors.cpp
index 8ee5c280b..a1cf2077f 100644
--- a/src/p_sectors.cpp
+++ b/src/p_sectors.cpp
@@ -1024,9 +1024,9 @@ CUSTOM_CVAR(Int, r_fakecontrast, true, CVAR_ARCHIVE|CVAR_GLOBALCONFIG)
 //
 //==========================================================================
 
-int side_t::GetLightLevel (bool foggy, int baselight, bool noabsolute, int *pfakecontrast) const
+int side_t::GetLightLevel (bool foggy, int baselight, bool is3dlight, int *pfakecontrast) const
 {
-	if (!noabsolute && (Flags & WALLF_ABSLIGHTING))
+	if (!is3dlight && (Flags & WALLF_ABSLIGHTING))
 	{
 		baselight = Light;
 	}
@@ -1066,7 +1066,7 @@ int side_t::GetLightLevel (bool foggy, int baselight, bool noabsolute, int *pfak
 			}
 		}
 	}
-	if (!(Flags & WALLF_ABSLIGHTING) && (!foggy || (Flags & WALLF_LIGHT_FOG)))
+	if (!is3dlight && !(Flags & WALLF_ABSLIGHTING) && (!foggy || (Flags & WALLF_LIGHT_FOG)))
 	{
 		baselight += this->Light;
 	}
diff --git a/src/r_segs.cpp b/src/r_segs.cpp
index 7bcfec13a..ebf525569 100644
--- a/src/r_segs.cpp
+++ b/src/r_segs.cpp
@@ -829,7 +829,7 @@ void R_RenderFakeWallRange (drawseg_t *ds, int x1, int x2)
 						{
 							lightlist_t *lit = &backsector->e->XFloor.lightlist[j];
 							basecolormap = lit->extra_colormap;
-							wallshade = LIGHT2SHADE(curline->sidedef->GetLightLevel(foggy, *lit->p_lightlevel, lit->lightsource == NULL) + r_actualextralight);
+							wallshade = LIGHT2SHADE(curline->sidedef->GetLightLevel(foggy, *lit->p_lightlevel, lit->lightsource != NULL) + r_actualextralight);
 							break;
 						}
 					}
@@ -842,7 +842,7 @@ void R_RenderFakeWallRange (drawseg_t *ds, int x1, int x2)
 						{
 							lightlist_t *lit = &frontsector->e->XFloor.lightlist[j];
 							basecolormap = lit->extra_colormap;
-							wallshade = LIGHT2SHADE(curline->sidedef->GetLightLevel(foggy, *lit->p_lightlevel, lit->lightsource == NULL) + r_actualextralight);
+							wallshade = LIGHT2SHADE(curline->sidedef->GetLightLevel(foggy, *lit->p_lightlevel, lit->lightsource != NULL) + r_actualextralight);
 							break;
 						}
 					}
diff --git a/src/thingdef/thingdef_codeptr.cpp b/src/thingdef/thingdef_codeptr.cpp
index 1764717f5..85f0c4675 100644
--- a/src/thingdef/thingdef_codeptr.cpp
+++ b/src/thingdef/thingdef_codeptr.cpp
@@ -3448,11 +3448,11 @@ DEFINE_ACTION_FUNCTION_PARAMS(AActor, A_CheckLOF)
 			}
 			else if (flags & CLOFF_AIM_VERT_NOOFFSET)
 			{
-				pitch += R_PointToAngle2 (0,0, xydist, target->Z() - pos.z + offsetheight + target->height / 2);
+				pitch -= R_PointToAngle2 (0,0, xydist, target->Z() - pos.z + offsetheight + target->height / 2);
 			}
 			else
 			{
-				pitch += R_PointToAngle2 (0,0, xydist, target->Z() - pos.z + target->height / 2);
+				pitch -= R_PointToAngle2 (0,0, xydist, target->Z() - pos.z + target->height / 2);
 			}
 		}
 		else if (flags & CLOFF_ALLOWNULL)
diff --git a/wadsrc/static/actors/actor.txt b/wadsrc/static/actors/actor.txt
index fab9ebd9f..08e376e61 100644
--- a/wadsrc/static/actors/actor.txt
+++ b/wadsrc/static/actors/actor.txt
@@ -82,9 +82,9 @@ ACTOR Actor native //: Thinker
 	action native A_XScream();
 	action native A_Look();
 	action native A_Chase(state melee = "*", state missile = "none", int flags = 0);
-	action native A_FaceTarget(float max_turn = 0, float max_pitch = 270, float ang_offset = 0, float pitch_offset = 0, int flags = 0);
-	action native A_FaceTracer(float max_turn = 0, float max_pitch = 270, float ang_offset = 0, float pitch_offset = 0, int flags = 0);
-	action native A_FaceMaster(float max_turn = 0, float max_pitch = 270, float ang_offset = 0, float pitch_offset = 0, int flags = 0);
+	action native A_FaceTarget(float max_turn = 0, float max_pitch = 270, float ang_offset = 0, float pitch_offset = 0, int flags = 0, float z_ofs = 0);
+	action native A_FaceTracer(float max_turn = 0, float max_pitch = 270, float ang_offset = 0, float pitch_offset = 0, int flags = 0, float z_ofs = 0);
+	action native A_FaceMaster(float max_turn = 0, float max_pitch = 270, float ang_offset = 0, float pitch_offset = 0, int flags = 0, float z_ofs = 0);
 	action native A_PosAttack();
 	action native A_Scream();
 	action native A_SPosAttack();