diff --git a/README.md b/README.md
new file mode 100644
index 0000000000..f04f324f7f
--- /dev/null
+++ b/README.md
@@ -0,0 +1,22 @@
+# Welcome to GZDoom!
+
+[![Build Status](https://ci.appveyor.com/api/projects/status/github/coelckers/gzdoom?branch=master&svg=true)](https://ci.appveyor.com/project/coelckers/gzdoom) [![Build Status](https://travis-ci.org/coelckers/gzdoom.svg?branch=master)](https://travis-ci.org/coelckers/gzdoom)
+
+## GZDoom is a modder-friendly OpenGL source port based on the DOOM engine
+
+Copyright (c) 1998-2018 ZDoom + GZDoom teams, and contributors
+
+Doom Source (c) 1997 id Software, Raven Software, and contributors
+
+Please see license files for individual contributor licenses
+
+Special thanks to Coraline of the 3DGE team for allowing us to use her README.md as a template for this one.
+
+### Licensed under the GPL v3 (or greater)
+##### https://www.gnu.org/licenses/quick-guide-gplv3.en.html
+---
+
+## How to build GZDoom
+
+To build GZDoom, please see the [wiki](https://zdoom.org/wiki/) and see the "Programmer's Corner" on the bottom-right corner of the page to build for your platform.
+
diff --git a/specs/udmf_zdoom.txt b/specs/udmf_zdoom.txt
index 1851604614..185d2a6def 100644
--- a/specs/udmf_zdoom.txt
+++ b/specs/udmf_zdoom.txt
@@ -283,6 +283,7 @@ Note: All <bool> fields default to false unless mentioned otherwise.
 
       For things with ACS specials (80-86 and 226), if arg0str is present and non-null, it
       will be used as the name of the script to execute, and arg0 will be ignored.
+	  On dynamic lights, arg0str can be used to set a color by name, this will supersede all args which are normally used to define a color.
    }
 
 
@@ -426,6 +427,9 @@ floor_reflect and ceiling_reflect.
 1.28 28.01.2017
 sector material colors.
 
+1.29 04.02.2018
+arg0str in dynamic lights.
+
 ===============================================================================
 EOF
 ===============================================================================
diff --git a/src/CMakeLists.txt b/src/CMakeLists.txt
index 8610691abc..5740e3f6e8 100644
--- a/src/CMakeLists.txt
+++ b/src/CMakeLists.txt
@@ -511,7 +511,7 @@ set( PLAT_SDL_SOURCES
 	posix/sdl/st_start.cpp )
 set( PLAT_UNIX_SOURCES
 	posix/unix/i_specialpaths.cpp
-	posix/unix/iwadpicker_gtk.cpp )
+	posix/unix/gtk_dialogs.cpp )
 set( PLAT_OSX_SOURCES
 	posix/osx/iwadpicker_cocoa.mm
 	posix/osx/i_specialpaths.mm
diff --git a/src/c_cmds.cpp b/src/c_cmds.cpp
index efc11a3d24..842516ba34 100644
--- a/src/c_cmds.cpp
+++ b/src/c_cmds.cpp
@@ -681,7 +681,7 @@ UNSAFE_CCMD (crashout)
 #endif
 
 
-CCMD (dir)
+UNSAFE_CCMD (dir)
 {
 	FString dir, path;
 	char curdir[256];
diff --git a/src/c_cvars.cpp b/src/c_cvars.cpp
index d51dacdcb0..7edf126ab8 100644
--- a/src/c_cvars.cpp
+++ b/src/c_cvars.cpp
@@ -53,6 +53,7 @@
 #include "colormatcher.h"
 #include "menu/menu.h"
 #include "vm.h"
+#include "v_text.h"
 
 struct FLatchedValue
 {
@@ -1706,6 +1707,16 @@ void C_ArchiveCVars (FConfigFile *f, uint32_t filter)
 
 EXTERN_CVAR(Bool, sv_cheats);
 
+static bool IsUnsafe(const FBaseCVar *const var)
+{
+	const bool unsafe = UnsafeExecutionContext && !(var->GetFlags() & CVAR_MOD);
+	if (unsafe)
+	{
+		Printf(TEXTCOLOR_RED "Cannot set console variable" TEXTCOLOR_GOLD " %s " TEXTCOLOR_RED "from unsafe command\n", var->GetName());
+	}
+	return unsafe;
+}
+
 void FBaseCVar::CmdSet (const char *newval)
 {
 	if ((GetFlags() & CVAR_CHEAT) && !sv_cheats)
@@ -1713,6 +1724,10 @@ void FBaseCVar::CmdSet (const char *newval)
 		Printf("sv_cheats must be true to set this console variable.\n");
 		return;
 	}
+	else if (IsUnsafe(this))
+	{
+		return;
+	}
 
 	UCVarValue val;
 
@@ -1799,6 +1814,11 @@ CCMD (toggle)
 	{
 		if ( (var = FindCVar (argv[1], &prev)) )
 		{
+			if (IsUnsafe(var))
+			{
+				return;
+			}
+
 			val = var->GetGenericRep (CVAR_Bool);
 			val.Bool = !val.Bool;
 			var->SetGenericRep (val, CVAR_Bool);
diff --git a/src/c_dispatch.cpp b/src/c_dispatch.cpp
index ec4571b53b..cb1fb47e1d 100644
--- a/src/c_dispatch.cpp
+++ b/src/c_dispatch.cpp
@@ -127,8 +127,24 @@ FButtonStatus Button_Mlook, Button_Klook, Button_Use, Button_AltAttack,
 	Button_AM_PanLeft, Button_AM_PanRight, Button_AM_PanDown, Button_AM_PanUp,
 	Button_AM_ZoomIn, Button_AM_ZoomOut;
 
-bool ParsingKeyConf;
-static bool UnsafeExecutionContext;
+bool ParsingKeyConf, UnsafeExecutionContext;
+
+class UnsafeExecutionScope
+{
+	const bool wasEnabled;
+
+public:
+	explicit UnsafeExecutionScope(const bool enable = true)
+	: wasEnabled(UnsafeExecutionContext)
+	{
+		UnsafeExecutionContext = enable;
+	}
+
+	~UnsafeExecutionScope()
+	{
+		UnsafeExecutionContext = wasEnabled;
+	}
+};
 
 // To add new actions, go to the console and type "key <action name>".
 // This will give you the key value to use in the first column. Then
@@ -227,10 +243,8 @@ void DWaitingCommand::Tick ()
 {
 	if (--TicsLeft == 0)
 	{
-		const bool wasUnsafe = UnsafeExecutionContext;
-		UnsafeExecutionContext = IsUnsafe;
+		UnsafeExecutionScope scope;
 		AddCommandString (Command);
-		UnsafeExecutionContext = wasUnsafe;
 		Destroy ();
 	}
 }
@@ -658,12 +672,6 @@ void C_DoCommand (const char *cmd, int keynum)
 
 			if (args.argc() >= 2)
 			{ // Set the variable
-				if (UnsafeExecutionContext && !(var->GetFlags() & CVAR_MOD))
-				{
-					Printf(TEXTCOLOR_RED "Cannot set console variable" TEXTCOLOR_GOLD " %s " TEXTCOLOR_RED "from unsafe command\n", var->GetName());
-					return;
-				}
-
 				var->CmdSet (args[1]);
 			}
 			else
@@ -684,9 +692,9 @@ DEFINE_ACTION_FUNCTION(DOptionMenuItemCommand, DoCommand)
 	if (CurrentMenu == nullptr) return 0;
 	PARAM_PROLOGUE;
 	PARAM_STRING(cmd);
-	UnsafeExecutionContext = true;
+	PARAM_BOOL(unsafe);
+	UnsafeExecutionScope scope(unsafe);
 	C_DoCommand(cmd);
-	UnsafeExecutionContext = false;
 	return 0;
 }
 
@@ -1515,9 +1523,8 @@ void FConsoleAlias::SafeDelete ()
 
 void FUnsafeConsoleAlias::Run (FCommandLine &args, APlayerPawn *instigator, int key)
 {
-	UnsafeExecutionContext = true;
+	UnsafeExecutionScope scope;
 	FConsoleAlias::Run(args, instigator, key);
-	UnsafeExecutionContext = false;
 }
 
 void FExecList::AddCommand(const char *cmd, const char *file)
diff --git a/src/c_dispatch.h b/src/c_dispatch.h
index dac14b818a..aa82e20ba9 100644
--- a/src/c_dispatch.h
+++ b/src/c_dispatch.h
@@ -200,7 +200,7 @@ extern FButtonStatus Button_Mlook, Button_Klook, Button_Use, Button_AltAttack,
 	Button_User1, Button_User2, Button_User3, Button_User4,
 	Button_AM_PanLeft, Button_AM_PanRight, Button_AM_PanDown, Button_AM_PanUp,
 	Button_AM_ZoomIn, Button_AM_ZoomOut;
-extern bool ParsingKeyConf;
+extern bool ParsingKeyConf, UnsafeExecutionContext;
 
 void ResetButtonTriggers ();	// Call ResetTriggers for all buttons
 void ResetButtonStates ();		// Same as above, but also clear bDown
diff --git a/src/dobjtype.cpp b/src/dobjtype.cpp
index 5f109e418c..275c3814eb 100644
--- a/src/dobjtype.cpp
+++ b/src/dobjtype.cpp
@@ -280,7 +280,7 @@ void PClass::StaticShutdown ()
 
 	// This must be done in two steps because the native classes are not ordered by inheritance,
 	// so all meta data must be gone before deleting the actual class objects.
-	for (auto cls : AllClasses)	cls->DestroyMeta(cls->Meta);
+	for (auto cls : AllClasses)	if (cls->Meta != nullptr) cls->DestroyMeta(cls->Meta);
 	for (auto cls : AllClasses)	delete cls;
 	// Unless something went wrong, anything left here should be class and type objects only, which do not own any scripts.
 	bShutdown = true;
diff --git a/src/g_game.cpp b/src/g_game.cpp
index 0e44e83016..d0cf74be7c 100644
--- a/src/g_game.cpp
+++ b/src/g_game.cpp
@@ -2599,7 +2599,7 @@ void G_DeferedPlayDemo (const char *name)
 	gameaction = (gameaction == ga_loadgame) ? ga_loadgameplaydemo : ga_playdemo;
 }
 
-CCMD (playdemo)
+UNSAFE_CCMD (playdemo)
 {
 	if (netgame)
 	{
diff --git a/src/g_inventory/a_weapons.cpp b/src/g_inventory/a_weapons.cpp
index 440c67f9b7..a0458ce3ea 100644
--- a/src/g_inventory/a_weapons.cpp
+++ b/src/g_inventory/a_weapons.cpp
@@ -220,7 +220,21 @@ void AWeapon::MarkPrecacheSounds() const
 //
 //===========================================================================
 
-bool AWeapon::CheckAmmo (int fireMode, bool autoSwitch, bool requireAmmo, int ammocount)
+bool AWeapon::CheckAmmo(int fireMode, bool autoSwitch, bool requireAmmo, int ammocount)
+{
+	IFVIRTUAL(AWeapon, CheckAmmo)
+	{
+		VMValue params[] = { (DObject*)this, fireMode, autoSwitch, requireAmmo, ammocount };
+		VMReturn ret;
+		int retval;
+		ret.IntAt(&retval);
+		VMCall(func, params, 5, &ret, 1);
+		return !!retval;
+	}
+	return CheckAmmo(fireMode, autoSwitch, requireAmmo, ammocount);
+}
+
+bool AWeapon::DoCheckAmmo (int fireMode, bool autoSwitch, bool requireAmmo, int ammocount)
 {
 	int altFire;
 	int count1, count2;
@@ -293,7 +307,7 @@ DEFINE_ACTION_FUNCTION(AWeapon, CheckAmmo)
 	PARAM_BOOL(autoswitch);
 	PARAM_BOOL_DEF(require);
 	PARAM_INT_DEF(ammocnt);
-	ACTION_RETURN_BOOL(self->CheckAmmo(mode, autoswitch, require, ammocnt));
+	ACTION_RETURN_BOOL(self->DoCheckAmmo(mode, autoswitch, require, ammocnt));
 }
 
 //===========================================================================
@@ -306,7 +320,21 @@ DEFINE_ACTION_FUNCTION(AWeapon, CheckAmmo)
 //
 //===========================================================================
 
-bool AWeapon::DepleteAmmo (bool altFire, bool checkEnough, int ammouse)
+bool AWeapon::DepleteAmmo(bool altFire, bool checkEnough, int ammouse)
+{
+	IFVIRTUAL(AWeapon, DepleteAmmo)
+	{
+		VMValue params[] = { (DObject*)this, altFire, checkEnough, ammouse };
+		VMReturn ret;
+		int retval;
+		ret.IntAt(&retval);
+		VMCall(func, params, 4, &ret, 1);
+		return !!retval;
+	}
+	return DoDepleteAmmo(altFire, checkEnough, ammouse);
+}
+
+bool AWeapon::DoDepleteAmmo (bool altFire, bool checkEnough, int ammouse)
 {
 	if (!((dmflags & DF_INFINITE_AMMO) || (Owner->FindInventory (PClass::FindActor(NAME_PowerInfiniteAmmo), true) != nullptr)))
 	{
@@ -357,7 +385,7 @@ DEFINE_ACTION_FUNCTION(AWeapon, DepleteAmmo)
 	PARAM_BOOL(altfire);
 	PARAM_BOOL_DEF(checkenough);
 	PARAM_INT_DEF(ammouse);
-	ACTION_RETURN_BOOL(self->DepleteAmmo(altfire, checkenough, ammouse));
+	ACTION_RETURN_BOOL(self->DoDepleteAmmo(altfire, checkenough, ammouse));
 }
 
 
diff --git a/src/g_inventory/a_weapons.h b/src/g_inventory/a_weapons.h
index 9b397e402c..4c6f6ab45f 100644
--- a/src/g_inventory/a_weapons.h
+++ b/src/g_inventory/a_weapons.h
@@ -142,7 +142,9 @@ public:
 		EitherFire
 	};
 	bool CheckAmmo (int fireMode, bool autoSwitch, bool requireAmmo=false, int ammocount = -1);
+	bool DoCheckAmmo(int fireMode, bool autoSwitch, bool requireAmmo, int ammocount);
 	bool DepleteAmmo (bool altFire, bool checkEnough=true, int ammouse = -1);
+	bool DoDepleteAmmo(bool altFire, bool checkEnough, int ammouse);
 
 	enum
 	{
diff --git a/src/g_level.cpp b/src/g_level.cpp
index 0b211f3e60..d6c712b241 100644
--- a/src/g_level.cpp
+++ b/src/g_level.cpp
@@ -648,7 +648,8 @@ void G_ChangeLevel(const char *levelname, int position, int flags, int nextSkill
 
 			// If this is co-op, respawn any dead players now so they can
 			// keep their inventory on the next map.
-			if ((multiplayer || level.flags2 & LEVEL2_ALLOWRESPAWN || sv_singleplayerrespawn) && !deathmatch && player->playerstate == PST_DEAD)
+			if ((multiplayer || level.flags2 & LEVEL2_ALLOWRESPAWN || sv_singleplayerrespawn || !!G_SkillProperty(SKILLP_PlayerRespawn))
+				&& !deathmatch && player->playerstate == PST_DEAD)
 			{
 				// Copied from the end of P_DeathThink [[
 				player->cls = NULL;		// Force a new class if the player is using a random class
@@ -2028,6 +2029,10 @@ DEFINE_FIELD(FLevelLocals, F1Pic)
 DEFINE_FIELD(FLevelLocals, maptype)
 DEFINE_FIELD(FLevelLocals, Music)
 DEFINE_FIELD(FLevelLocals, musicorder)
+DEFINE_FIELD(FLevelLocals, skytexture1)
+DEFINE_FIELD(FLevelLocals, skytexture2)
+DEFINE_FIELD(FLevelLocals, skyspeed1)
+DEFINE_FIELD(FLevelLocals, skyspeed2)
 DEFINE_FIELD(FLevelLocals, total_secrets)
 DEFINE_FIELD(FLevelLocals, found_secrets)
 DEFINE_FIELD(FLevelLocals, total_items)
@@ -2093,3 +2098,19 @@ CCMD(skyfog)
 	}
 }
 
+
+//==========================================================================
+//
+// ZScript counterpart to ACS ChangeSky, uses TextureIDs
+//
+//==========================================================================
+DEFINE_ACTION_FUNCTION(FLevelLocals, ChangeSky)
+{
+	PARAM_SELF_STRUCT_PROLOGUE(FLevelLocals);
+	PARAM_INT(sky1);
+	PARAM_INT(sky2);
+	sky1texture = self->skytexture1 = FSetTextureID(sky1);
+	sky2texture = self->skytexture2 = FSetTextureID(sky2);
+	R_InitSkyMap();
+	return 0;
+}
diff --git a/src/gl/scene/gl_decal.cpp b/src/gl/scene/gl_decal.cpp
index cf23102094..0f3bc7ffb4 100644
--- a/src/gl/scene/gl_decal.cpp
+++ b/src/gl/scene/gl_decal.cpp
@@ -289,7 +289,7 @@ void GLWall::DrawDecal(DBaseDecal *decal)
 		// Note: This should be replaced with proper shader based lighting.
 		double x, y;
 		decal->GetXY(seg->sidedef, x, y);
-		gl_SetDynSpriteLight(NULL, x, y, zpos, sub);
+		gl_SetDynSpriteLight(nullptr, x, y, zpos - decalheight * 0.5f, sub);
 	}
 
 	// alpha color only has an effect when using an alpha texture.
diff --git a/src/gl/scene/gl_scene.cpp b/src/gl/scene/gl_scene.cpp
index a0bcb48821..178b39ff7c 100644
--- a/src/gl/scene/gl_scene.cpp
+++ b/src/gl/scene/gl_scene.cpp
@@ -842,7 +842,7 @@ sector_t * GLSceneDrawer::RenderViewpoint (AActor * camera, GL_IRECT * bounds, f
 	stereo3dMode.SetUp();
 	for (int eye_ix = 0; eye_ix < stereo3dMode.eye_count(); ++eye_ix)
 	{
-		if (eye_ix > 0)
+		if (eye_ix > 0 && camera->player)
 			SetFixedColormap(camera->player); // reiterate color map for each eye, so night vision goggles work in both eyes
 		const s3d::EyePose * eye = stereo3dMode.getEyePose(eye_ix);
 		eye->SetUp();
diff --git a/src/gl/scene/gl_sprite.cpp b/src/gl/scene/gl_sprite.cpp
index ac7eccac3f..a1816acd21 100644
--- a/src/gl/scene/gl_sprite.cpp
+++ b/src/gl/scene/gl_sprite.cpp
@@ -987,9 +987,8 @@ void GLSprite::Process(AActor* thing, sector_t * sector, int thruportal)
 		RenderStyle.CheckFuzz();
 		if (RenderStyle.BlendOp == STYLEOP_Fuzz)
 		{
-			if (gl_fuzztype != 0 && !gl.legacyMode)
+			if (gl_fuzztype != 0 && !gl.legacyMode && !(RenderStyle.Flags & STYLEF_InvertSource))
 			{
-				// Todo: implement shader selection here
 				RenderStyle = LegacyRenderStyles[STYLE_Translucent];
 				OverrideShader = SHADER_NoTexture + gl_fuzztype;
 				trans = 0.99f;	// trans may not be 1 here
diff --git a/src/gl/scene/gl_spritelight.cpp b/src/gl/scene/gl_spritelight.cpp
index ac7e6971e5..1415ce16c9 100644
--- a/src/gl/scene/gl_spritelight.cpp
+++ b/src/gl/scene/gl_spritelight.cpp
@@ -74,7 +74,7 @@ void gl_SetDynSpriteLight(AActor *self, float x, float y, float z, subsector_t *
 	while (node)
 	{
 		light=node->lightsource;
-		if (light->visibletoplayer && !(light->flags2&MF2_DORMANT) && (!(light->lightflags&LF_DONTLIGHTSELF) || light->target != self) && !(light->lightflags&LF_DONTLIGHTACTORS))
+		if (light->visibletoplayer && !(light->flags2&MF2_DORMANT) && (!(light->lightflags&LF_DONTLIGHTSELF) || light->target != self || !self) && !(light->lightflags&LF_DONTLIGHTACTORS))
 		{
 			float dist;
 			FVector3 L;
diff --git a/src/gl/stereo3d/gl_stereo_cvars.cpp b/src/gl/stereo3d/gl_stereo_cvars.cpp
index 201e33590e..e7ce699f55 100644
--- a/src/gl/stereo3d/gl_stereo_cvars.cpp
+++ b/src/gl/stereo3d/gl_stereo_cvars.cpp
@@ -32,6 +32,7 @@
 #include "gl/stereo3d/gl_sidebyside3d.h"
 #include "gl/stereo3d/gl_interleaved3d.h"
 #include "gl/system/gl_cvars.h"
+#include "version.h"
 
 // Set up 3D-specific console variables:
 CVAR(Int, vr_mode, 0, CVAR_GLOBALCONFIG)
@@ -42,7 +43,10 @@ CVAR(Bool, vr_swap_eyes, false, CVAR_GLOBALCONFIG)
 // For broadest GL compatibility, require user to explicitly enable quad-buffered stereo mode.
 // Setting vr_enable_quadbuffered_stereo does not automatically invoke quad-buffered stereo,
 // but makes it possible for subsequent "vr_mode 7" to invoke quad-buffered stereo
-CVAR(Bool, vr_enable_quadbuffered, false, CVAR_ARCHIVE | CVAR_GLOBALCONFIG)
+CUSTOM_CVAR(Bool, vr_enable_quadbuffered, false, CVAR_ARCHIVE | CVAR_GLOBALCONFIG | CVAR_NOINITCALL)
+{
+	Printf("You must restart " GAMENAME " to switch quad stereo mode\n");
+}
 
 // intraocular distance in meters
 CVAR(Float, vr_ipd, 0.062f, CVAR_ARCHIVE|CVAR_GLOBALCONFIG) // METERS
diff --git a/src/m_misc.cpp b/src/m_misc.cpp
index eb51ec7b9a..481f956b51 100644
--- a/src/m_misc.cpp
+++ b/src/m_misc.cpp
@@ -673,7 +673,7 @@ void M_ScreenShot (const char *filename)
 	}
 }
 
-CCMD (screenshot)
+UNSAFE_CCMD (screenshot)
 {
 	if (argv.argc() == 1)
 		G_ScreenShot (NULL);
diff --git a/src/menu/menu.cpp b/src/menu/menu.cpp
index 86ec78abf2..f03c37eb73 100644
--- a/src/menu/menu.cpp
+++ b/src/menu/menu.cpp
@@ -58,6 +58,7 @@
 #include "vm.h"
 #include "events.h"
 #include "gl/renderer/gl_renderer.h" // for menu blur
+#include "scripting/types.h"
 
 //
 // Todo: Move these elsewhere
@@ -1180,6 +1181,8 @@ DMenuItemBase * CreateOptionMenuItemCommand(const char *label, FName cmd, bool c
 	VMValue params[] = { p, &namestr, cmd.GetIndex(), centered };
 	auto f = dyn_cast<PFunction>(c->FindSymbol("Init", false));
 	VMCall(f->Variants[0].Implementation, params, countof(params), nullptr, 0);
+	auto unsafe = dyn_cast<PField>(c->FindSymbol("mUnsafe", false));
+	unsafe->Type->SetValue(reinterpret_cast<uint8_t*>(p) + unsafe->Offset, 0);
 	return (DMenuItemBase*)p;
 }
 
diff --git a/src/p_acs.cpp b/src/p_acs.cpp
index e2fccad141..e36cecde78 100644
--- a/src/p_acs.cpp
+++ b/src/p_acs.cpp
@@ -835,12 +835,12 @@ inline int uallong(const int &foo)
 //============================================================================
 
 // ACS variables with world scope
-int32_t ACS_WorldVars[NUM_WORLDVARS];
-FWorldGlobalArray ACS_WorldArrays[NUM_WORLDVARS];
+static BoundsCheckingArray<int32_t, NUM_WORLDVARS> ACS_WorldVars;
+static BoundsCheckingArray<FWorldGlobalArray, NUM_WORLDVARS> ACS_WorldArrays;
 
 // ACS variables with global scope
-int32_t ACS_GlobalVars[NUM_GLOBALVARS];
-FWorldGlobalArray ACS_GlobalArrays[NUM_GLOBALVARS];
+BoundsCheckingArray<int32_t, NUM_GLOBALVARS> ACS_GlobalVars;
+BoundsCheckingArray<FWorldGlobalArray, NUM_GLOBALVARS> ACS_GlobalArrays;
 
 //----------------------------------------------------------------------------
 //
@@ -851,21 +851,7 @@ FWorldGlobalArray ACS_GlobalArrays[NUM_GLOBALVARS];
 //
 //----------------------------------------------------------------------------
 
-struct FACSStackMemory
-{
-	int32_t& operator[](const size_t index)
-	{
-		if (index >= STACK_SIZE)
-		{
-			I_Error("Corrupted stack pointer in ACS VM");
-		}
-
-		return buffer[index];
-	}
-
-private:
-	int32_t buffer[STACK_SIZE];
-};
+using FACSStackMemory = BoundsCheckingArray<int32_t, STACK_SIZE>;
 
 struct FACSStack
 {
@@ -1470,10 +1456,10 @@ void ACSStringPool::UnlockForLevel(int lnum)
 
 void P_MarkWorldVarStrings()
 {
-	GlobalACSStrings.MarkStringArray(ACS_WorldVars, countof(ACS_WorldVars));
-	for (size_t i = 0; i < countof(ACS_WorldArrays); ++i)
+	GlobalACSStrings.MarkStringArray(ACS_WorldVars.Pointer(), ACS_WorldVars.Size());
+	for (size_t i = 0; i < ACS_WorldArrays.Size(); ++i)
 	{
-		GlobalACSStrings.MarkStringMap(ACS_WorldArrays[i]);
+		GlobalACSStrings.MarkStringMap(ACS_WorldArrays.Pointer()[i]);
 	}
 }
 
@@ -1485,10 +1471,10 @@ void P_MarkWorldVarStrings()
 
 void P_MarkGlobalVarStrings()
 {
-	GlobalACSStrings.MarkStringArray(ACS_GlobalVars, countof(ACS_GlobalVars));
-	for (size_t i = 0; i < countof(ACS_GlobalArrays); ++i)
+	GlobalACSStrings.MarkStringArray(ACS_GlobalVars.Pointer(), ACS_GlobalVars.Size());
+	for (size_t i = 0; i < ACS_GlobalArrays.Size(); ++i)
 	{
-		GlobalACSStrings.MarkStringMap(ACS_GlobalArrays[i]);
+		GlobalACSStrings.MarkStringMap(ACS_GlobalArrays.Pointer()[i]);
 	}
 }
 
@@ -1571,14 +1557,14 @@ void P_ClearACSVars(bool alsoglobal)
 {
 	int i;
 
-	memset (ACS_WorldVars, 0, sizeof(ACS_WorldVars));
+	ACS_WorldVars.Fill(0);
 	for (i = 0; i < NUM_WORLDVARS; ++i)
 	{
 		ACS_WorldArrays[i].Clear ();
 	}
 	if (alsoglobal)
 	{
-		memset (ACS_GlobalVars, 0, sizeof(ACS_GlobalVars));
+		ACS_GlobalVars.Fill(0);
 		for (i = 0; i < NUM_GLOBALVARS; ++i)
 		{
 			ACS_GlobalArrays[i].Clear ();
@@ -1726,10 +1712,10 @@ static void ReadArrayVars (FSerializer &file, FWorldGlobalArray *vars, size_t co
 
 void P_ReadACSVars(FSerializer &arc)
 {
-	ReadVars (arc, ACS_WorldVars, NUM_WORLDVARS, "acsworldvars");
-	ReadVars (arc, ACS_GlobalVars, NUM_GLOBALVARS, "acsglobalvars");
-	ReadArrayVars (arc, ACS_WorldArrays, NUM_WORLDVARS, "acsworldarrays");
-	ReadArrayVars (arc, ACS_GlobalArrays, NUM_GLOBALVARS, "acsglobalarrays");
+	ReadVars (arc, ACS_WorldVars.Pointer(), NUM_WORLDVARS, "acsworldvars");
+	ReadVars (arc, ACS_GlobalVars.Pointer(), NUM_GLOBALVARS, "acsglobalvars");
+	ReadArrayVars (arc, ACS_WorldArrays.Pointer(), NUM_WORLDVARS, "acsworldarrays");
+	ReadArrayVars (arc, ACS_GlobalArrays.Pointer(), NUM_GLOBALVARS, "acsglobalarrays");
 	GlobalACSStrings.ReadStrings(arc, "acsglobalstrings");
 }
 
@@ -1741,10 +1727,10 @@ void P_ReadACSVars(FSerializer &arc)
 
 void P_WriteACSVars(FSerializer &arc)
 {
-	WriteVars (arc, ACS_WorldVars, NUM_WORLDVARS, "acsworldvars");
-	WriteVars (arc, ACS_GlobalVars, NUM_GLOBALVARS, "acsglobalvars");
-	WriteArrayVars (arc, ACS_WorldArrays, NUM_WORLDVARS, "acsworldarrays");
-	WriteArrayVars (arc, ACS_GlobalArrays, NUM_GLOBALVARS, "acsglobalarrays");
+	WriteVars (arc, ACS_WorldVars.Pointer(), NUM_WORLDVARS, "acsworldvars");
+	WriteVars (arc, ACS_GlobalVars.Pointer(), NUM_GLOBALVARS, "acsglobalvars");
+	WriteArrayVars (arc, ACS_WorldArrays.Pointer(), NUM_WORLDVARS, "acsworldarrays");
+	WriteArrayVars (arc, ACS_GlobalArrays.Pointer(), NUM_GLOBALVARS, "acsglobalarrays");
 	GlobalACSStrings.WriteStrings(arc, "acsglobalstrings");
 }
 
@@ -9852,7 +9838,7 @@ scriptwait:
 			if (STACK(2) != 0)
 			{
 				AActor *marine;
-				NActorIterator iterator("ScriptedMarine", STACK(2));
+				NActorIterator iterator(NAME_ScriptedMarine, STACK(2));
 
 				while ((marine = iterator.Next()) != NULL)
 				{
@@ -9861,7 +9847,7 @@ scriptwait:
 			}
 			else
 			{
-				if (activator != nullptr && activator->IsKindOf (PClass::FindClass("ScriptedMarine")))
+				if (activator != nullptr && activator->IsKindOf (NAME_ScriptedMarine))
 				{
 					SetMarineWeapon(activator, STACK(1));
 				}
@@ -9878,7 +9864,7 @@ scriptwait:
 					if (STACK(2) != 0)
 					{
 						AActor *marine;
-						NActorIterator iterator("ScriptedMarine", STACK(2));
+						NActorIterator iterator(NAME_ScriptedMarine, STACK(2));
 
 						while ((marine = iterator.Next()) != NULL)
 						{
@@ -9887,7 +9873,7 @@ scriptwait:
 					}
 					else
 					{
-						if (activator != nullptr && activator->IsKindOf("ScriptedMarine"))
+						if (activator != nullptr && activator->IsKindOf(NAME_ScriptedMarine))
 						{
 							SetMarineSprite(activator, type);
 						}
diff --git a/src/p_acs.h b/src/p_acs.h
index 4f53ce1a37..7b0d18bd82 100644
--- a/src/p_acs.h
+++ b/src/p_acs.h
@@ -60,13 +60,32 @@ struct InitIntToZero
 };
 typedef TMap<int32_t, int32_t, THashTraits<int32_t>, InitIntToZero> FWorldGlobalArray;
 
-// ACS variables with world scope
-extern int32_t ACS_WorldVars[NUM_WORLDVARS];
-extern FWorldGlobalArray ACS_WorldArrays[NUM_WORLDVARS];
+// Type of elements count is unsigned int instead of size_t to match ACSStringPool interface
+template <typename T, unsigned int N>
+struct BoundsCheckingArray
+{
+	T &operator[](const unsigned int index)
+	{
+		if (index >= N)
+		{
+			I_Error("Out of bounds memory access in ACS VM");
+		}
+
+		return buffer[index];
+	}
+
+	T *Pointer() { return buffer; }
+	unsigned int Size() const { return N; }
+
+	void Fill(const T &value) { std::fill(std::begin(buffer), std::end(buffer), value); }
+
+private:
+	T buffer[N];
+};
 
 // ACS variables with global scope
-extern int32_t ACS_GlobalVars[NUM_GLOBALVARS];
-extern FWorldGlobalArray ACS_GlobalArrays[NUM_GLOBALVARS];
+extern BoundsCheckingArray<int32_t, NUM_GLOBALVARS> ACS_GlobalVars;
+extern BoundsCheckingArray<FWorldGlobalArray, NUM_GLOBALVARS> ACS_GlobalArrays;
 
 #define LIBRARYID_MASK			0xFFF00000
 #define LIBRARYID_SHIFT			20
@@ -359,7 +378,7 @@ public:
 	ACSProfileInfo *GetFunctionProfileData(ScriptFunction *func) { return GetFunctionProfileData((int)(func - (ScriptFunction *)Functions)); }
 	const char *LookupString (uint32_t index) const;
 
-	int32_t *MapVars[NUM_MAPVARS];
+	BoundsCheckingArray<int32_t *, NUM_MAPVARS> MapVars;
 
 	static FBehavior *StaticLoadModule (int lumpnum, FileReader * fr=NULL, int len=0);
 	static void StaticLoadDefaultModules ();
diff --git a/src/p_glnodes.cpp b/src/p_glnodes.cpp
index bd574ad837..60c666e82a 100644
--- a/src/p_glnodes.cpp
+++ b/src/p_glnodes.cpp
@@ -1216,7 +1216,7 @@ errorout:
 	return false;
 }
 
-CCMD(clearnodecache)
+UNSAFE_CCMD(clearnodecache)
 {
 	TArray<FFileList> list;
 	FString path = M_GetCachePath(false);
diff --git a/src/p_maputl.cpp b/src/p_maputl.cpp
index 24c30375e2..6b19942e0f 100644
--- a/src/p_maputl.cpp
+++ b/src/p_maputl.cpp
@@ -809,11 +809,13 @@ bool FMultiBlockLinesIterator::GoUp(double x, double y)
 	{
 		if (!cursector->PortalBlocksMovement(sector_t::ceiling))
 		{
-			startIteratorForGroup(cursector->GetOppositePortalGroup(sector_t::ceiling));
-			portalflags = FFCF_NOFLOOR;
-			return true;
+			if (startIteratorForGroup(cursector->GetOppositePortalGroup(sector_t::ceiling)))
+			{
+				portalflags = FFCF_NOFLOOR;
+				return true;
+			}
 		}
-		else continueup = false;
+		continueup = false;
 	}
 	return false;
 }
@@ -830,11 +832,13 @@ bool FMultiBlockLinesIterator::GoDown(double x, double y)
 	{
 		if (!cursector->PortalBlocksMovement(sector_t::floor))
 		{
-			startIteratorForGroup(cursector->GetOppositePortalGroup(sector_t::floor));
-			portalflags = FFCF_NOCEILING;
-			return true;
+			if (startIteratorForGroup(cursector->GetOppositePortalGroup(sector_t::floor)))
+			{
+				portalflags = FFCF_NOCEILING;
+				return true;
+			}
 		}
-		else continuedown = false;
+		continuedown = false;
 	}
 	return false;
 }
@@ -906,14 +910,19 @@ bool FMultiBlockLinesIterator::Next(FMultiBlockLinesIterator::CheckResult *item)
 //
 //===========================================================================
 
-void FMultiBlockLinesIterator::startIteratorForGroup(int group)
+bool FMultiBlockLinesIterator::startIteratorForGroup(int group)
 {
 	offset = Displacements.getOffset(basegroup, group);
 	offset.X += checkpoint.X;
 	offset.Y += checkpoint.Y;
 	cursector = group == startsector->PortalGroup ? startsector : P_PointInSector(offset);
+	// If we ended up in a different group, 
+	// presumably because the spot to be checked is too far outside the actual portal group,
+	// the search needs to abort.
+	if (cursector->PortalGroup != group) return false;
 	bbox.setBox(offset.X, offset.Y, checkpoint.Z);
 	blockIterator.init(bbox);
+	return true;
 }
 
 //===========================================================================
diff --git a/src/p_maputl.h b/src/p_maputl.h
index 8ac3ea76af..4dfa99e0f0 100644
--- a/src/p_maputl.h
+++ b/src/p_maputl.h
@@ -240,7 +240,7 @@ class FMultiBlockLinesIterator
 
 	bool GoUp(double x, double y);
 	bool GoDown(double x, double y);
-	void startIteratorForGroup(int group);
+	bool startIteratorForGroup(int group);
 
 public:
 
diff --git a/src/p_mobj.cpp b/src/p_mobj.cpp
index 79f549dd38..8e5e1d3a26 100644
--- a/src/p_mobj.cpp
+++ b/src/p_mobj.cpp
@@ -6101,6 +6101,9 @@ AActor *P_SpawnMapThing (FMapThing *mthing, int position)
 		if (mthing->arg0str != NAME_None)
 		{
 			PalEntry color = V_GetColor(nullptr, mthing->arg0str);
+			light->args[0] = color.r;
+			light->args[1] = color.g;
+			light->args[2] = color.b;
 		}
 		else if (light->lightflags & LF_SPOT)
 		{
@@ -7766,7 +7769,13 @@ FState *AActor::GetRaiseState()
 void AActor::Revive()
 {
 	AActor *info = GetDefault();
+	FLinkContext ctx;
+
+	bool flagchange = (flags & (MF_NOBLOCKMAP | MF_NOSECTOR)) != (info->flags & (MF_NOBLOCKMAP | MF_NOSECTOR));
+
+	if (flagchange) UnlinkFromWorld(&ctx);
 	flags = info->flags;
+	if (flagchange) LinkToWorld(&ctx);
 	flags2 = info->flags2;
 	flags3 = info->flags3;
 	flags4 = info->flags4;
diff --git a/src/p_sectors.cpp b/src/p_sectors.cpp
index 369c5de61b..fb4789e17e 100644
--- a/src/p_sectors.cpp
+++ b/src/p_sectors.cpp
@@ -1659,7 +1659,7 @@ DEFINE_ACTION_FUNCTION(_Sector, NextLowestFloorAt)
 	 PARAM_SELF_STRUCT_PROLOGUE(sector_t);
 	 PARAM_INT(pos);
 	 PARAM_FLOAT(o);
-	 self->SetXScale(pos, o);
+	 self->SetYScale(pos, o);
 	 return 0;
  }
 
diff --git a/src/p_trace.cpp b/src/p_trace.cpp
index d00a5c4cc0..fd79861ec2 100644
--- a/src/p_trace.cpp
+++ b/src/p_trace.cpp
@@ -955,8 +955,8 @@ static bool EditTraceResult (uint32_t flags, FTraceResults &res)
 //  [ZZ] here go the methods for the ZScript interface
 //
 //==========================================================================
-IMPLEMENT_CLASS(DTracer, false, false)
-DEFINE_FIELD_X(Tracer, DTracer, Results)
+IMPLEMENT_CLASS(DLineTracer, false, false)
+DEFINE_FIELD(DLineTracer, Results)
 
 // define TraceResults fields
 DEFINE_FIELD_NAMED_X(TraceResults, FTraceResults, Sector, HitSector)
@@ -978,9 +978,9 @@ DEFINE_FIELD_X(TraceResults, FTraceResults, CrossedWaterPos)
 DEFINE_FIELD_X(TraceResults, FTraceResults, Crossed3DWater)
 DEFINE_FIELD_X(TraceResults, FTraceResults, Crossed3DWaterPos)
 
-DEFINE_ACTION_FUNCTION(DTracer, Trace)
+DEFINE_ACTION_FUNCTION(DLineTracer, Trace)
 {
-	PARAM_SELF_PROLOGUE(DTracer);
+	PARAM_SELF_PROLOGUE(DLineTracer);
 	/*bool Trace(const DVector3 &start, sector_t *sector, const DVector3 &direction, double maxDist,
 	ActorFlags ActorMask, uint32_t WallMask, AActor *ignore, FTraceResults &res, uint32_t traceFlags = 0,
 	ETraceStatus(*callback)(FTraceResults &res, void *) = NULL, void *callbackdata = NULL);*/
@@ -1001,13 +1001,13 @@ DEFINE_ACTION_FUNCTION(DTracer, Trace)
 
 	// Trace(vector3 start, Sector sector, vector3 direction, double maxDist, ETraceFlags traceFlags)
 	bool res = Trace(DVector3(start_x, start_y, start_z), sector, DVector3(direction_x, direction_y, direction_z), maxDist,
-					 (ActorFlag)0xFFFFFFFF, 0xFFFFFFFF, nullptr, self->Results, traceFlags, &DTracer::TraceCallback, self);
+					 (ActorFlag)0xFFFFFFFF, 0xFFFFFFFF, nullptr, self->Results, traceFlags, &DLineTracer::TraceCallback, self);
 	ACTION_RETURN_BOOL(res);
 }
 
-ETraceStatus DTracer::TraceCallback(FTraceResults& res, void* pthis)
+ETraceStatus DLineTracer::TraceCallback(FTraceResults& res, void* pthis)
 {
-	DTracer* self = (DTracer*)pthis;
+	DLineTracer* self = (DLineTracer*)pthis;
 	// "res" here should refer to self->Results anyway.
 
 	// patch results a bit. modders don't expect it to work like this most likely.
@@ -1036,13 +1036,13 @@ ETraceStatus DTracer::TraceCallback(FTraceResults& res, void* pthis)
 	return self->CallZScriptCallback();
 }
 
-ETraceStatus DTracer::CallZScriptCallback()
+ETraceStatus DLineTracer::CallZScriptCallback()
 {
-	IFVIRTUAL(DTracer, TraceCallback)
+	IFVIRTUAL(DLineTracer, TraceCallback)
 	{
 		int status;
 		VMReturn results[1] = { &status };
-		VMValue params[1] = { (DTracer*)this };
+		VMValue params[1] = { (DLineTracer*)this };
 		VMCall(func, params, 1, results, 1);
 		return (ETraceStatus)status;
 	}
diff --git a/src/p_trace.h b/src/p_trace.h
index af4187f785..0a61cc7258 100644
--- a/src/p_trace.h
+++ b/src/p_trace.h
@@ -113,9 +113,9 @@ bool Trace(const DVector3 &start, sector_t *sector, const DVector3 &direction, d
 	ETraceStatus(*callback)(FTraceResults &res, void *) = NULL, void *callbackdata = NULL);
 
 // [ZZ] this is the object that's used for ZScript
-class DTracer : public DObject
+class DLineTracer : public DObject
 {
-	DECLARE_CLASS(DTracer, DObject)
+	DECLARE_CLASS(DLineTracer, DObject)
 public:
 	FTraceResults Results;
 	static ETraceStatus TraceCallback(FTraceResults& res, void* pthis);
diff --git a/src/posix/sdl/i_main.cpp b/src/posix/sdl/i_main.cpp
index 21f58e71e9..95ed8322eb 100644
--- a/src/posix/sdl/i_main.cpp
+++ b/src/posix/sdl/i_main.cpp
@@ -73,6 +73,10 @@ extern "C" int cc_install_handlers(int, char**, int, int*, const char*, int(*)(c
 void Mac_I_FatalError(const char* errortext);
 #endif
 
+#ifdef __linux__
+void Linux_I_FatalError(const char* errortext);
+#endif
+
 // PUBLIC FUNCTION PROTOTYPES ----------------------------------------------
 
 // PRIVATE FUNCTION PROTOTYPES ---------------------------------------------
@@ -268,6 +272,10 @@ int main (int argc, char **argv)
 		Mac_I_FatalError(error.GetMessage());
 #endif // __APPLE__
 
+#ifdef __linux__
+		Linux_I_FatalError(error.GetMessage());
+#endif // __linux__
+
 		exit (-1);
     }
     catch (...)
diff --git a/src/posix/sdl/i_system.cpp b/src/posix/sdl/i_system.cpp
index b71acb8f8d..f980e25983 100644
--- a/src/posix/sdl/i_system.cpp
+++ b/src/posix/sdl/i_system.cpp
@@ -79,6 +79,7 @@ extern "C"
 #ifndef NO_GTK
 bool I_GtkAvailable ();
 int I_PickIWad_Gtk (WadStuff *wads, int numwads, bool showwin, int defaultiwad);
+void I_FatalError_Gtk(const char* errortext);
 #elif defined(__APPLE__)
 int I_PickIWad_Cocoa (WadStuff *wads, int numwads, bool showwin, int defaultiwad);
 #endif
@@ -157,6 +158,37 @@ bool gameisdead;
 void Mac_I_FatalError(const char* errortext);
 #endif
 
+#ifdef __linux__
+void Linux_I_FatalError(const char* errortext)
+{
+	// Close window or exit fullscreen and release mouse capture
+	SDL_Quit();
+
+	const char *str;
+	if((str=getenv("KDE_FULL_SESSION")) && strcmp(str, "true") == 0)
+	{
+		FString cmd;
+		cmd << "kdialog --title \"" GAMESIG " ";
+		cmd << GetVersionString() << ": No IWAD found\" ";
+		cmd << "--msgbox \"" << errortext << "\"";
+		popen(cmd, "r");
+	}
+#ifndef NO_GTK
+	else if (I_GtkAvailable())
+	{
+		I_FatalError_Gtk(errortext);
+	}
+#endif
+	else
+	{
+		FString message;
+		message << GAMESIG " ";
+		message << GetVersionString() << ": No IWAD found";
+		SDL_ShowSimpleMessageBox(SDL_MESSAGEBOX_ERROR, message, errortext, NULL);
+	}
+}
+#endif
+
 void I_FatalError (const char *error, ...)
 {
     static bool alreadyThrown = false;
@@ -175,6 +207,10 @@ void I_FatalError (const char *error, ...)
 #ifdef __APPLE__
 		Mac_I_FatalError(errortext);
 #endif // __APPLE__		
+
+#ifdef __linux__
+		Linux_I_FatalError(errortext);
+#endif
 		
 		// Record error to log (if logging)
 		if (Logfile)
diff --git a/src/posix/unix/iwadpicker_gtk.cpp b/src/posix/unix/gtk_dialogs.cpp
similarity index 83%
rename from src/posix/unix/iwadpicker_gtk.cpp
rename to src/posix/unix/gtk_dialogs.cpp
index ebaab609f8..658f8cbc5d 100644
--- a/src/posix/unix/iwadpicker_gtk.cpp
+++ b/src/posix/unix/gtk_dialogs.cpp
@@ -1,5 +1,5 @@
 /*
-** iwadpicker_gtk.cpp
+** gtk_dialogs.cpp
 **
 **---------------------------------------------------------------------------
 ** Copyright 2008-2016 Braden Obrzut
@@ -126,12 +126,16 @@ DYN_GTK_SYM(gtk_window_new);
 DYN_GTK_SYM(gtk_window_set_gravity);
 DYN_GTK_SYM(gtk_window_set_position);
 DYN_GTK_SYM(gtk_window_set_title);
+DYN_GTK_SYM(gtk_window_set_resizable);
+DYN_GTK_SYM(gtk_dialog_run);
+DYN_GTK_SYM(gtk_dialog_get_type);
 
 // Gtk3 Only
 DYN_GTK_OPT3_SYM(gtk_box_new, GtkWidget *(*)(GtkOrientation, gint));
 DYN_GTK_OPT3_SYM(gtk_button_box_new, GtkWidget *(*)(GtkOrientation));
 DYN_GTK_OPT3_SYM(gtk_widget_set_halign, void(*)(GtkWidget *, GtkAlign));
 DYN_GTK_OPT3_SYM(gtk_widget_set_valign, void(*)(GtkWidget *, GtkAlign));
+DYN_GTK_OPT3_SYM(gtk_message_dialog_new, GtkWidget* (*)(GtkWindow*, GtkDialogFlags, GtkMessageType, GtkButtonsType, const gchar*, ...));
 
 // Gtk2 Only
 DYN_GTK_OPT2_SYM(gtk_misc_get_type, GType(*)());
@@ -342,6 +346,70 @@ static int PickIWad (WadStuff *wads, int numwads, bool showwin, int defaultiwad)
 	return i;
 }
 
+static void ShowError(const char* errortext)
+{
+	GtkWidget *window;
+	GtkWidget *widget;
+	GtkWidget *vbox = nullptr;
+	GtkWidget *bbox = nullptr;
+
+	window = gtk_window_new (GTK_WINDOW_TOPLEVEL);
+	gtk_window_set_title (GTK_WINDOW(window), "Fatal error");
+	gtk_window_set_position (GTK_WINDOW(window), GTK_WIN_POS_CENTER);
+	gtk_window_set_gravity (GTK_WINDOW(window), GDK_GRAVITY_CENTER);
+	gtk_window_set_resizable (GTK_WINDOW(window), false);
+	gtk_container_set_border_width (GTK_CONTAINER(window), 10);
+	g_signal_connect (window, "delete_event", G_CALLBACK(gtk_main_quit), NULL);
+	g_signal_connect (window, "key_press_event", G_CALLBACK(CheckEscape), NULL);
+
+	// Create the vbox container.
+	if (gtk_box_new) // Gtk3
+		vbox = gtk_box_new (GTK_ORIENTATION_VERTICAL, 10);
+	else if (gtk_vbox_new) // Gtk2
+		vbox = gtk_vbox_new (FALSE, 10);
+
+	gtk_container_add (GTK_CONTAINER(window), vbox);
+
+	// Create the label.
+	widget = gtk_label_new ((const gchar *) errortext);
+	gtk_box_pack_start (GTK_BOX(vbox), widget, false, false, 0);
+
+	if (gtk_widget_set_halign && gtk_widget_set_valign) // Gtk3
+	{
+		gtk_widget_set_halign (widget, GTK_ALIGN_START);
+		gtk_widget_set_valign (widget, GTK_ALIGN_START);
+	}
+	else if (gtk_misc_set_alignment && gtk_misc_get_type) // Gtk2
+		gtk_misc_set_alignment (GTK_MISC(widget), 0, 0);
+
+	// Create the Exit button box.
+	if (gtk_button_box_new) // Gtk3
+		bbox = gtk_button_box_new (GTK_ORIENTATION_HORIZONTAL);
+	else if (gtk_hbutton_box_new) // Gtk2
+		bbox = gtk_hbutton_box_new ();
+
+	gtk_button_box_set_layout (GTK_BUTTON_BOX(bbox), GTK_BUTTONBOX_END);
+	gtk_box_set_spacing (GTK_BOX(bbox), 10);
+	gtk_box_pack_end (GTK_BOX(vbox), bbox, false, false, 0);
+
+	// Create the cancel button.
+	widget = gtk_button_new_with_label ("Exit");
+	gtk_box_pack_start (GTK_BOX(bbox), widget, false, false, 0);
+	g_signal_connect (widget, "clicked", G_CALLBACK(gtk_main_quit), &window);
+
+	// Finally we can show everything.
+	gtk_widget_show_all (window);
+
+	gtk_main ();
+
+	if (GTK_IS_WINDOW(window))
+	{
+		gtk_widget_destroy (window);
+		// If we don't do this, then the X window might not actually disappear.
+		while (g_main_context_iteration (NULL, FALSE)) {}
+	}
+}
+
 } // namespace Gtk
 
 int I_PickIWad_Gtk (WadStuff *wads, int numwads, bool showwin, int defaultiwad)
@@ -349,6 +417,10 @@ int I_PickIWad_Gtk (WadStuff *wads, int numwads, bool showwin, int defaultiwad)
 	return Gtk::PickIWad (wads, numwads, showwin, defaultiwad);
 }
 
+void I_FatalError_Gtk(const char* errortext) {
+	Gtk::ShowError(errortext);
+}
+
 bool I_GtkAvailable()
 {
 	using namespace Gtk;
diff --git a/src/s_sound.cpp b/src/s_sound.cpp
index fede842b10..d3f587b948 100644
--- a/src/s_sound.cpp
+++ b/src/s_sound.cpp
@@ -2999,7 +2999,7 @@ CCMD (cd_resume)
 //
 //==========================================================================
 
-CCMD (playlist)
+UNSAFE_CCMD (playlist)
 {
 	int argc = argv.argc();
 
diff --git a/src/sound/mididevices/music_fluidsynth_mididevice.cpp b/src/sound/mididevices/music_fluidsynth_mididevice.cpp
index 07102c43d6..42244b61a7 100644
--- a/src/sound/mididevices/music_fluidsynth_mididevice.cpp
+++ b/src/sound/mididevices/music_fluidsynth_mididevice.cpp
@@ -124,13 +124,13 @@ CUSTOM_CVAR(Float, fluid_gain, 0.5, CVAR_ARCHIVE|CVAR_GLOBALCONFIG)
 		currSong->FluidSettingNum("synth.gain", self);
 }
 
-CUSTOM_CVAR(Bool, fluid_reverb, true, CVAR_ARCHIVE|CVAR_GLOBALCONFIG)
+CUSTOM_CVAR(Bool, fluid_reverb, false, CVAR_ARCHIVE|CVAR_GLOBALCONFIG)
 {
 	if (currSong != NULL)
 		currSong->FluidSettingInt("synth.reverb.active", self);
 }
 
-CUSTOM_CVAR(Bool, fluid_chorus, true, CVAR_ARCHIVE|CVAR_GLOBALCONFIG)
+CUSTOM_CVAR(Bool, fluid_chorus, false, CVAR_ARCHIVE|CVAR_GLOBALCONFIG)
 {
 	if (currSong != NULL)
 		currSong->FluidSettingInt("synth.chorus.active", self);
diff --git a/src/textures/texturemanager.cpp b/src/textures/texturemanager.cpp
index 5039f48b60..613aa3be9f 100644
--- a/src/textures/texturemanager.cpp
+++ b/src/textures/texturemanager.cpp
@@ -1206,8 +1206,21 @@ DEFINE_ACTION_FUNCTION(_TexMan, GetName)
 {
 	PARAM_PROLOGUE;
 	PARAM_INT(texid);
-	const FTexture* const tex = TexMan.ByIndex(texid);
-	ACTION_RETURN_STRING(nullptr == tex ? FString() : tex->Name);
+	auto tex = TexMan.ByIndex(texid);
+	FString retval;
+
+	if (tex != nullptr)
+	{
+		if (tex->Name.IsNotEmpty()) retval = tex->Name;
+		else
+		{
+			// Textures for full path names do not have their own name, they merely link to the source lump.
+			auto lump = tex->GetSourceLump();
+			if (Wads.GetLinkedTexture(lump) == tex)
+				retval = Wads.GetLumpFullName(lump);
+		}
+	}
+	ACTION_RETURN_STRING(retval);
 }
 
 //==========================================================================
diff --git a/wadsrc/static/compatibility.txt b/wadsrc/static/compatibility.txt
index 245c450529..b78b4e6648 100644
--- a/wadsrc/static/compatibility.txt
+++ b/wadsrc/static/compatibility.txt
@@ -376,6 +376,14 @@ F481922F4881F74760F3C0437FD5EDD0 // map03
 	setlinespecial 1008 Door_Open 0 64 0 0 0
 }
 
+7ED9800213C00D6E7FB98652AB48B3DE // Ultimate Simplicity, map04
+{
+	// Add missing map spots on easy and medium skills
+	// Demons will teleport into starting room making 100% kills possible
+	setthingskills 31 31
+	setthingskills 32 31
+}
+
 1891E029994B023910CFE0B3209C3CDB // Ultimate Simplicity, map07
 {
 	// It is possible to get stuck on skill 0 or 1 when no shots have been fired
@@ -386,6 +394,13 @@ F481922F4881F74760F3C0437FD5EDD0 // map03
 	setlinespecial 411 NoiseAlert 0 0 0 0 0
 }
 
+F0E6F30F57B0425F17E43600AA813E80 // Ultimate Simplicity, map11
+{
+	// If door (sector #309) is closed it cannot be open again
+	// from one side potentially blocking level progression
+	clearlinespecial 2445
+}
+
 952CC8D03572E17BA550B01B366EFBB9 // Cheogsh map01
 {
 	// make the blue key spawn above the 3D floor
@@ -685,6 +700,10 @@ EBDAC00E9D25D884B2C8F4B1F0390539 // doom2.wad map21
 	setsectoroffset 50 ceil -56
 	setsectoroffset 54 ceil -56
 }
+94893A0DC429A22ADC4B3A73DA537E16 // DOOM2.WAD map25
+{
+   rebuildnodes
+}
 110F84DE041052B59307FAF0293E6BC0 // Doom II, map27
 {
 	setsectorspecial 93 0
@@ -844,3 +863,8 @@ CA3773ED313E8899311F3DD0CA195A68 // e3m6
 	setthingz 403 168
 	setthingz 404 168
 }
+
+6D4156EE0D12B77AD143A37C4D3DCF98 // dmonfear.wad map22
+{
+	shorttex
+}
diff --git a/wadsrc/static/credits/rsmk.txt b/wadsrc/static/credits/rsmk.txt
new file mode 100644
index 0000000000..e37c200866
--- /dev/null
+++ b/wadsrc/static/credits/rsmk.txt
@@ -0,0 +1,3 @@
+These sprites were made by Talon1024 and have been put in the public domain:
+
+https://forum.zdoom.org/viewtopic.php?f=15&t=59245
diff --git a/wadsrc/static/language.enu b/wadsrc/static/language.enu
index 7b5eed9a05..5014365528 100644
--- a/wadsrc/static/language.enu
+++ b/wadsrc/static/language.enu
@@ -2729,7 +2729,7 @@ GLPREFMNU_AMBLIGHT 				= "Ambient light level";
 GLPREFMNU_RENDERQUALITY 		= "Rendering quality";
 GLPREFMNU_MENUBLUR				= "Menu Blur";
 GLPREFMNU_VRMODE 				= "Stereo 3D VR";
-GLPREFMNU_VRQUADSTEREO 			= "Enable Quad Stereo (Requires Restart)";
+GLPREFMNU_VRQUADSTEREO 			= "Enable Quad Stereo";
 GLPREFMNU_MULTISAMPLE			= "Multisample";
 GLPREFMNU_TONEMAP				= "Tonemap Mode";
 GLPREFMNU_BLOOM					= "Bloom effect";
diff --git a/wadsrc/static/mapinfo/common.txt b/wadsrc/static/mapinfo/common.txt
index 1c1559b061..b79ecd5f4f 100644
--- a/wadsrc/static/mapinfo/common.txt
+++ b/wadsrc/static/mapinfo/common.txt
@@ -118,7 +118,7 @@ DoomEdNums
   9851 = SpotLightPulseAdditive
   9852 = SpotLightFlickerAdditive
   9853 = SectorSpotLightAdditive
-  9854 = SpotLightFlickerRandomSubtractive
+  9854 = SpotLightFlickerRandomAdditive
   9860 = SpotLightSubtractive
   9861 = SpotLightPulseSubtractive
   9862 = SpotLightFlickerSubtractive
diff --git a/wadsrc/static/shaders/glsl/fuzz_software.fp b/wadsrc/static/shaders/glsl/fuzz_software.fp
index 4fe4ab669e..7840ce8be4 100644
--- a/wadsrc/static/shaders/glsl/fuzz_software.fp
+++ b/wadsrc/static/shaders/glsl/fuzz_software.fp
@@ -5,8 +5,8 @@
 #define FRACBITS 16
 #define fixed_t int
 
-int fuzz_random_x_offset[FUZZ_RANDOM_X_SIZE] =
-{
+int fuzz_random_x_offset[FUZZ_RANDOM_X_SIZE] = int[]
+(
 	75, 76, 21, 91, 56, 33, 62, 99, 61, 79,
 	95, 54, 41, 18, 69, 43, 49, 59, 10, 84,
 	94, 17, 57, 46,  9, 39, 55, 34,100, 81,
@@ -17,16 +17,16 @@ int fuzz_random_x_offset[FUZZ_RANDOM_X_SIZE] =
 	65, 15, 97, 20, 67, 74, 98, 85, 60, 68,
 	19, 26,  8, 87, 86, 64, 11, 37, 31, 47,
 	25,  5, 50, 51, 23,  2, 93, 70, 40, 45
-};
+);
 
-int fuzzoffset[FUZZTABLE] =
-{
+int fuzzoffset[FUZZTABLE] = int[]
+(
 	 6, 11,  6, 11,  6,  6, 11,  6,  6, 11,
 	 6,  6,  6, 11,  6,  6,  6, 11, 15, 18,
 	21,  6, 11, 15,  6,  6,  6,  6, 11, 6,
 	11,  6,  6, 11, 15,  6,  6, 11, 15, 18,
 	21,  6,  6,  6,  6, 11,  6,  6, 11, 6
-};
+);
 
 vec4 ProcessTexel()
 {
diff --git a/wadsrc/static/sprites/rsmka0.png b/wadsrc/static/sprites/rsmka0.png
new file mode 100644
index 0000000000..8387c22445
Binary files /dev/null and b/wadsrc/static/sprites/rsmka0.png differ
diff --git a/wadsrc/static/sprites/rsmkb0.png b/wadsrc/static/sprites/rsmkb0.png
new file mode 100644
index 0000000000..7417f79823
Binary files /dev/null and b/wadsrc/static/sprites/rsmkb0.png differ
diff --git a/wadsrc/static/sprites/rsmkc0.png b/wadsrc/static/sprites/rsmkc0.png
new file mode 100644
index 0000000000..d1ec180687
Binary files /dev/null and b/wadsrc/static/sprites/rsmkc0.png differ
diff --git a/wadsrc/static/sprites/rsmkd0.png b/wadsrc/static/sprites/rsmkd0.png
new file mode 100644
index 0000000000..08d3c95e53
Binary files /dev/null and b/wadsrc/static/sprites/rsmkd0.png differ
diff --git a/wadsrc/static/sprites/rsmke0.png b/wadsrc/static/sprites/rsmke0.png
new file mode 100644
index 0000000000..ab4ddb55ad
Binary files /dev/null and b/wadsrc/static/sprites/rsmke0.png differ
diff --git a/wadsrc/static/zscript/base.txt b/wadsrc/static/zscript/base.txt
index bef1751da8..5d30435b59 100644
--- a/wadsrc/static/zscript/base.txt
+++ b/wadsrc/static/zscript/base.txt
@@ -524,7 +524,7 @@ struct TraceResults native
 	native vector3 Crossed3DWaterPos;
 }
 
-class Tracer : Object native
+class LineTracer : Object native
 {
 	native @TraceResults Results;
 	native bool Trace(vector3 start, Sector sec, vector3 direction, double maxDist, ETraceFlags traceFlags);
@@ -591,6 +591,10 @@ struct LevelLocals native
 	native readonly int maptype;
 	native readonly String Music;
 	native readonly int musicorder;
+	native readonly TextureID skytexture1;
+	native readonly TextureID skytexture2;
+	native float skyspeed1;
+	native float skyspeed2;
 	native int total_secrets;
 	native int found_secrets;
 	native int total_items;
@@ -640,7 +644,9 @@ struct LevelLocals native
 	native static clearscope vector3 Vec3Diff(vector3 v1, vector3 v2);
 
 	native String GetChecksum() const;
-	
+
+	native void ChangeSky( TextureID sky1, TextureID sky2 );
+
 	String TimeFormatted(bool totals = false)
 	{
 		int sec = Thinker.Tics2Seconds(totals? totaltime : time); 
diff --git a/wadsrc/static/zscript/inventory/weapons.txt b/wadsrc/static/zscript/inventory/weapons.txt
index f837bf4e54..4786e44d7a 100644
--- a/wadsrc/static/zscript/inventory/weapons.txt
+++ b/wadsrc/static/zscript/inventory/weapons.txt
@@ -78,8 +78,8 @@ class Weapon : StateProvider native
 		Stop;
 	}
 	
-	native bool CheckAmmo(int fireMode, bool autoSwitch, bool requireAmmo = false, int ammocount = -1);
-	native bool DepleteAmmo(bool altFire, bool checkEnough = true, int ammouse = -1);
+	native virtual bool CheckAmmo(int fireMode, bool autoSwitch, bool requireAmmo = false, int ammocount = -1);
+	native virtual bool DepleteAmmo(bool altFire, bool checkEnough = true, int ammouse = -1);
 	
 	virtual State GetReadyState ()
 	{
diff --git a/wadsrc/static/zscript/menu/optionmenuitems.txt b/wadsrc/static/zscript/menu/optionmenuitems.txt
index 4668ea0681..00fe4893cc 100644
--- a/wadsrc/static/zscript/menu/optionmenuitems.txt
+++ b/wadsrc/static/zscript/menu/optionmenuitems.txt
@@ -128,16 +128,18 @@ class OptionMenuItemCommand : OptionMenuItemSubmenu
 {
 	private String ccmd;	// do not allow access to this from the outside.
 	bool mCloseOnSelect;
+	private bool mUnsafe;
 	
 	OptionMenuItemCommand Init(String label, Name command, bool centered = false, bool closeonselect = false)
 	{
 		Super.Init(label, command, 0, centered);
 		ccmd = command;
 		mCloseOnSelect = closeonselect;
+		mUnsafe = true;
 		return self;
 	}
 
-	private native static void DoCommand(String cmd);	// This is very intentionally limited to this menu item to prevent abuse.
+	private native static void DoCommand(String cmd, bool unsafe);	// This is very intentionally limited to this menu item to prevent abuse.
 
 	override bool Activate()
 	{
@@ -151,7 +153,7 @@ class OptionMenuItemCommand : OptionMenuItemSubmenu
 			if (m.GetItem(mAction) != self) return false;
 		}
 		Menu.MenuSound("menu/choose");
-		DoCommand(ccmd);
+		DoCommand(ccmd, mUnsafe);
 		if (mCloseOnSelect)
 		{
 			let curmenu = Menu.GetCurrentMenu();
diff --git a/wadsrc/static/zscript/shared/player.txt b/wadsrc/static/zscript/shared/player.txt
index d43a59ce27..8ecce11cb2 100644
--- a/wadsrc/static/zscript/shared/player.txt
+++ b/wadsrc/static/zscript/shared/player.txt
@@ -528,7 +528,7 @@ class PlayerPawn : Actor native
 			if (level.time >= player.respawn_time || ((player.cmd.buttons & BT_USE) && player.Bot == NULL))
 			{
 				player.cls = NULL;		// Force a new class if the player is using a random class
-				player.playerstate = (multiplayer || (level.AllowRespawn) || sv_singleplayerrespawn)? PST_REBORN : PST_ENTER;
+				player.playerstate = (multiplayer || level.AllowRespawn || sv_singleplayerrespawn || G_SkillPropertyInt(SKILLP_PlayerRespawn)) ? PST_REBORN : PST_ENTER;
 				if (special1 > 2)
 				{
 					special1 = 0;
diff --git a/wadsrc_extra/static/sprites/rsmka0.png b/wadsrc_extra/static/sprites/rsmka0.png
deleted file mode 100644
index 761e091709..0000000000
Binary files a/wadsrc_extra/static/sprites/rsmka0.png and /dev/null differ
diff --git a/wadsrc_extra/static/sprites/rsmkb0.png b/wadsrc_extra/static/sprites/rsmkb0.png
deleted file mode 100644
index 0bcfef43da..0000000000
Binary files a/wadsrc_extra/static/sprites/rsmkb0.png and /dev/null differ
diff --git a/wadsrc_extra/static/sprites/rsmkc0.png b/wadsrc_extra/static/sprites/rsmkc0.png
deleted file mode 100644
index 3e952cdba9..0000000000
Binary files a/wadsrc_extra/static/sprites/rsmkc0.png and /dev/null differ
diff --git a/wadsrc_extra/static/sprites/rsmkd0.png b/wadsrc_extra/static/sprites/rsmkd0.png
deleted file mode 100644
index 60827b6dcb..0000000000
Binary files a/wadsrc_extra/static/sprites/rsmkd0.png and /dev/null differ
diff --git a/wadsrc_extra/static/sprites/rsmke0.png b/wadsrc_extra/static/sprites/rsmke0.png
deleted file mode 100644
index 9d5652bd25..0000000000
Binary files a/wadsrc_extra/static/sprites/rsmke0.png and /dev/null differ