diff --git a/src/b_bot.h b/src/b_bot.h
index fd3ad3c94..27433b533 100644
--- a/src/b_bot.h
+++ b/src/b_bot.h
@@ -10,7 +10,7 @@
 #include "c_cvars.h"
 #include "info.h"
 #include "doomdef.h"
-#include "d_ticcmd.h"
+#include "d_protocol.h"
 #include "r_defs.h"
 #include "a_pickups.h"
 #include "stats.h"
diff --git a/src/b_move.cpp b/src/b_move.cpp
index 2a3d40bcb..0354be8bf 100644
--- a/src/b_move.cpp
+++ b/src/b_move.cpp
@@ -10,7 +10,7 @@
 #include "p_local.h"
 #include "b_bot.h"
 #include "g_game.h"
-#include "d_ticcmd.h"
+#include "d_protocol.h"
 #include "m_random.h"
 #include "i_system.h"
 #include "p_lnspec.h"
diff --git a/src/c_bind.cpp b/src/c_bind.cpp
index 8d27c38bd..65cdc1757 100644
--- a/src/c_bind.cpp
+++ b/src/c_bind.cpp
@@ -45,6 +45,7 @@
 #include "d_event.h"
 #include "w_wad.h"
 #include "templates.h"
+#include "dobject.h"
 
 #include <math.h>
 #include <stdlib.h>
diff --git a/src/d_net.h b/src/d_net.h
index def8dee06..282f73e15 100644
--- a/src/d_net.h
+++ b/src/d_net.h
@@ -25,7 +25,7 @@
 
 #include "doomtype.h"
 #include "doomdef.h"
-#include "d_ticcmd.h"
+#include "d_protocol.h"
 
 
 //
diff --git a/src/d_netinf.h b/src/d_netinf.h
index 4f0f6e403..c5c82f65b 100644
--- a/src/d_netinf.h
+++ b/src/d_netinf.h
@@ -36,8 +36,6 @@
 
 #include "c_cvars.h"
 
-EXTERN_CVAR (Float, autoaim)
-
 int D_GenderToInt (const char *gender);
 extern const char *GenderNames[3];
 
diff --git a/src/d_player.h b/src/d_player.h
index 66a2ce547..4a718778b 100644
--- a/src/d_player.h
+++ b/src/d_player.h
@@ -26,7 +26,7 @@
 // Finally, for odd reasons, the player input
 // is buffered within the player data struct,
 // as commands per game tick.
-#include "d_ticcmd.h"
+#include "d_protocol.h"
 #include "doomstat.h"
 
 #include "a_weapons.h"
diff --git a/src/d_protocol.cpp b/src/d_protocol.cpp
index 36ec2cab2..06caca46c 100644
--- a/src/d_protocol.cpp
+++ b/src/d_protocol.cpp
@@ -33,7 +33,7 @@
 */
 
 #include "i_system.h"
-#include "d_ticcmd.h"
+#include "d_protocol.h"
 #include "d_net.h"
 #include "doomdef.h"
 #include "doomstat.h"
diff --git a/src/d_protocol.h b/src/d_protocol.h
index 7de26a179..5ac1258b3 100644
--- a/src/d_protocol.h
+++ b/src/d_protocol.h
@@ -229,7 +229,15 @@ int UnpackUserCmd (usercmd_t *ucmd, const usercmd_t *basis, uint8_t **stream);
 int PackUserCmd (const usercmd_t *ucmd, const usercmd_t *basis, uint8_t **stream);
 int WriteUserCmdMessage (usercmd_t *ucmd, const usercmd_t *basis, uint8_t **stream);
 
-struct ticcmd_t;
+// The data sampled per tick (single player)
+// and transmitted to other peers (multiplayer).
+// Mainly movements/button commands per game tick,
+// plus a checksum for internal state consistency.
+struct ticcmd_t
+{
+	usercmd_t	ucmd;
+	int16_t		consistancy;	// checks for net game
+};
 
 int SkipTicCmd (uint8_t **stream, int count);
 void ReadTicCmd (uint8_t **stream, int player, int tic);
diff --git a/src/d_ticcmd.h b/src/d_ticcmd.h
deleted file mode 100644
index 66a629e08..000000000
--- a/src/d_ticcmd.h
+++ /dev/null
@@ -1,38 +0,0 @@
-// Emacs style mode select	 -*- C++ -*- 
-//-----------------------------------------------------------------------------
-//
-// $Id:$
-//
-// Copyright (C) 1993-1996 by id Software, Inc.
-//
-// This source is available for distribution and/or modification
-// only under the terms of the DOOM Source Code License as
-// published by id Software. All rights reserved.
-//
-// The source is distributed in the hope that it will be useful,
-// but WITHOUT ANY WARRANTY; without even the implied warranty of
-// FITNESS FOR A PARTICULAR PURPOSE. See the DOOM Source Code License
-// for more details.
-//
-// DESCRIPTION:
-//		System specific interface stuff.
-//
-//-----------------------------------------------------------------------------
-
-
-#ifndef __D_TICCMD_H__
-#define __D_TICCMD_H__
-
-#include "d_protocol.h"
-
-// The data sampled per tick (single player)
-// and transmitted to other peers (multiplayer).
-// Mainly movements/button commands per game tick,
-// plus a checksum for internal state consistency.
-struct ticcmd_t
-{
-	usercmd_t	ucmd;
-	int16_t		consistancy;	// checks for net game
-};
-
-#endif	// __D_TICCMD_H__
diff --git a/src/decallib.h b/src/decallib.h
index 7c3369c4d..75df4ae42 100644
--- a/src/decallib.h
+++ b/src/decallib.h
@@ -38,7 +38,6 @@
 
 #include "doomtype.h"
 #include "r_data/renderstyle.h"
-#include "textures/textures.h"
 
 class FScanner;
 class FDecalTemplate;
diff --git a/src/dobjgc.cpp b/src/dobjgc.cpp
index 56e8c82d4..35a30c136 100644
--- a/src/dobjgc.cpp
+++ b/src/dobjgc.cpp
@@ -65,7 +65,6 @@
 #include "sbar.h"
 #include "stats.h"
 #include "c_dispatch.h"
-#include "p_acs.h"
 #include "s_sndseq.h"
 #include "r_data/r_interpolate.h"
 #include "doomstat.h"
@@ -80,6 +79,8 @@
 #include "g_levellocals.h"
 #include "events.h"
 
+void MarkACSThinker();
+
 // MACROS ------------------------------------------------------------------
 
 /*
@@ -331,7 +332,7 @@ static void MarkRoot()
 	Mark(DIntermissionController::CurrentIntermission);
 	DThinker::MarkRoots();
 	FCanvasTextureInfo::Mark();
-	Mark(DACSThinker::ActiveThinker);
+	MarkACSThinker();
 	Mark(E_FirstEventHandler);
 	Mark(E_LastEventHandler);
 	for (auto &s : level.sectorPortals)
diff --git a/src/dobjtype.h b/src/dobjtype.h
index 6b24610f8..c3ced5a63 100644
--- a/src/dobjtype.h
+++ b/src/dobjtype.h
@@ -8,6 +8,13 @@
 typedef std::pair<const class PType *, unsigned> FTypeAndOffset;
 class PStruct;
 
+// This is intentionally not in vm.h so that this file remains free of DObject pollution.
+class VMException : public DObject
+{
+	DECLARE_CLASS(VMException, DObject);
+};
+
+
 #include "vm.h"
 
 // Variable/parameter/field flags -------------------------------------------
diff --git a/src/dscript.h b/src/dscript.h
deleted file mode 100644
index 725f9b77b..000000000
--- a/src/dscript.h
+++ /dev/null
@@ -1,26 +0,0 @@
-enum
-{
-	EX_Return		= 0x00,
-	EX_EndFuncParms	= 0x01,
-	EX_ByteConst	= 0x02,
-	EX_WordConst	= 0x03,
-	EX_DWordConst	= 0x04,
-	EX_FixedConst	= 0x05,		// To become FloatConst whenever I move to floats
-	EX_StringConst	= 0x06,
-
-	EX_Extended1	= 0xF1,
-	EX_Extended2	= 0xF2,
-	EX_Extended3	= 0xF3,
-	EX_Extended4	= 0xF4,
-	EX_Extended5	= 0xF5,
-	EX_Extended6	= 0xF6,
-	EX_Extended7	= 0xF7,
-	EX_Extended8	= 0xF8,
-	EX_Extended9	= 0xF9,
-	EX_ExtendedA	= 0xFA,
-	EX_ExtendedB	= 0xFB,
-	EX_ExtendedC	= 0xFC,
-	EX_ExtendedD	= 0xFD,
-	EX_ExtendedE	= 0xFE,
-	EX_ExtendedF	= 0xFF
-};
\ No newline at end of file
diff --git a/src/g_level.h b/src/g_level.h
index ccb00b0ee..db2fd6cc1 100644
--- a/src/g_level.h
+++ b/src/g_level.h
@@ -35,16 +35,12 @@
 #define __G_LEVEL_H__
 
 #include "doomtype.h"
-#include "doomdef.h"
 #include "sc_man.h"
-#include "s_sound.h"
-#include "p_acs.h"
-#include "textures/textures.h"
 #include "resourcefiles/file_zip.h"
 
 struct level_info_t;
 struct cluster_info_t;
-class FScanner;
+class FSerializer;
 
 #if defined(_MSC_VER)
 #pragma section(".yreg$u",read)
@@ -55,6 +51,24 @@ class FScanner;
 #define GCC_YSEG __attribute__((section(SECTION_YREG))) __attribute__((used))
 #endif
 
+// The structure used to control scripts between maps
+struct acsdefered_t
+{
+	enum EType
+	{
+		defexecute,
+		defexealways,
+		defsuspend,
+		defterminate
+	} type;
+	int script;
+	int args[3];
+	int playernum;
+};
+
+FSerializer &Serialize(FSerializer &arc, const char *key, acsdefered_t &defer, acsdefered_t *def);
+
+
 struct FIntermissionDescriptor;
 struct FIntermissionAction;
 
@@ -339,7 +353,7 @@ struct level_info_t
 
 	TArray<FSpecialAction> specialactions;
 
-	TArray<FSoundID> PrecacheSounds;
+	TArray<int> PrecacheSounds;
 	TArray<FString> PrecacheTextures;
 	TArray<FName> PrecacheClasses;
 	
diff --git a/src/g_pch.h b/src/g_pch.h
index e5653796b..cad5a8409 100644
--- a/src/g_pch.h
+++ b/src/g_pch.h
@@ -21,3 +21,10 @@
 #include <limits>
 #include <memory>
 #include <tuple>
+#include <vector>
+#include <utility>
+
+// These two headers get included nearly everywhere so it doesn't matter if changing them forces a few more recompiles.
+// The overall savings from PCHing them are more significant.
+#include "tarray.h"
+#include "zstring.h"
\ No newline at end of file
diff --git a/src/gi.cpp b/src/gi.cpp
index ad5c5a0ee..d30902045 100644
--- a/src/gi.cpp
+++ b/src/gi.cpp
@@ -125,6 +125,21 @@ const char* GameInfoBorders[] =
 		} \
 		while (sc.CheckToken(',')); \
 	}
+#define GAMEINFOKEY_SOUNDARRAY(key, variable, length, clear) \
+	else if(nextKey.CompareNoCase(variable) == 0) \
+	{ \
+		if (clear) gameinfo.key.Clear(); \
+		do \
+		{ \
+			sc.MustGetToken(TK_StringConst); \
+			if(length > 0 && strlen(sc.String) > length) \
+			{ \
+				sc.ScriptError("Value for '%s' can not be longer than %d characters.", #key, length); \
+			} \
+			gameinfo.key[gameinfo.key.Reserve(1)] = FSoundID(sc.String); \
+		} \
+		while (sc.CheckToken(',')); \
+	}
 
 #define GAMEINFOKEY_STRING(key, variable) \
 	else if(nextKey.CompareNoCase(variable) == 0) \
@@ -323,7 +338,7 @@ void FMapInfoParser::ParseGameInfo()
 		GAMEINFOKEY_STRINGARRAY(infoPages, "infoPage", 8, true)
 		GAMEINFOKEY_STRINGARRAY(PrecachedClasses, "precacheclasses", 0, false)
 		GAMEINFOKEY_STRINGARRAY(PrecachedTextures, "precachetextures", 0, false)
-		GAMEINFOKEY_STRINGARRAY(PrecachedSounds, "precachesounds", 0, false)
+		GAMEINFOKEY_SOUNDARRAY(PrecachedSounds, "precachesounds", 0, false)
 		GAMEINFOKEY_STRINGARRAY(EventHandlers, "addeventhandlers", 0, true)
 		GAMEINFOKEY_STRINGARRAY(EventHandlers, "eventhandlers", 0, false)
 		GAMEINFOKEY_STRING(PauseSign, "pausesign")
diff --git a/src/gi.h b/src/gi.h
index f20ae0d99..759637dea 100644
--- a/src/gi.h
+++ b/src/gi.h
@@ -36,7 +36,6 @@
 
 #include "basictypes.h"
 #include "zstring.h"
-#include "s_sound.h"
 
 // Flags are not user configurable and only depend on the standard IWADs
 #define GI_MAPxx				0x00000001
@@ -123,7 +122,7 @@ struct gameinfo_t
 
 	TArray<FName> PrecachedClasses;
 	TArray<FString> PrecachedTextures;
-	TArray<FSoundID> PrecachedSounds;
+	TArray<int> PrecachedSounds;
 	TArray<FString> EventHandlers;
 
 	FString titleMusic;
diff --git a/src/gl/renderer/gl_renderbuffers.cpp b/src/gl/renderer/gl_renderbuffers.cpp
index fad79767c..a3635ca0b 100644
--- a/src/gl/renderer/gl_renderbuffers.cpp
+++ b/src/gl/renderer/gl_renderbuffers.cpp
@@ -26,7 +26,6 @@
 */
 
 #include "gl/system/gl_system.h"
-#include "files.h"
 #include "m_swap.h"
 #include "v_video.h"
 #include "gl/gl_functions.h"
diff --git a/src/gl/shaders/gl_ambientshader.cpp b/src/gl/shaders/gl_ambientshader.cpp
index effde2496..02090cf61 100644
--- a/src/gl/shaders/gl_ambientshader.cpp
+++ b/src/gl/shaders/gl_ambientshader.cpp
@@ -21,7 +21,6 @@
 //
 
 #include "gl/system/gl_system.h"
-#include "files.h"
 #include "m_swap.h"
 #include "v_video.h"
 #include "gl/gl_functions.h"
diff --git a/src/gl/shaders/gl_bloomshader.cpp b/src/gl/shaders/gl_bloomshader.cpp
index 44253ae79..bc7b80b01 100644
--- a/src/gl/shaders/gl_bloomshader.cpp
+++ b/src/gl/shaders/gl_bloomshader.cpp
@@ -26,7 +26,6 @@
 */
 
 #include "gl/system/gl_system.h"
-#include "files.h"
 #include "m_swap.h"
 #include "v_video.h"
 #include "gl/gl_functions.h"
diff --git a/src/gl/shaders/gl_blurshader.cpp b/src/gl/shaders/gl_blurshader.cpp
index cd4532cc4..56b637f6d 100644
--- a/src/gl/shaders/gl_blurshader.cpp
+++ b/src/gl/shaders/gl_blurshader.cpp
@@ -26,7 +26,6 @@
 */
 
 #include "gl/system/gl_system.h"
-#include "files.h"
 #include "m_swap.h"
 #include "v_video.h"
 #include "gl/gl_functions.h"
diff --git a/src/gl/shaders/gl_colormapshader.cpp b/src/gl/shaders/gl_colormapshader.cpp
index 06c72160a..e29b27013 100644
--- a/src/gl/shaders/gl_colormapshader.cpp
+++ b/src/gl/shaders/gl_colormapshader.cpp
@@ -26,7 +26,6 @@
 */
 
 #include "gl/system/gl_system.h"
-#include "files.h"
 #include "m_swap.h"
 #include "v_video.h"
 #include "gl/gl_functions.h"
diff --git a/src/gl/shaders/gl_lensshader.cpp b/src/gl/shaders/gl_lensshader.cpp
index 9d242aa87..c5ec679f3 100644
--- a/src/gl/shaders/gl_lensshader.cpp
+++ b/src/gl/shaders/gl_lensshader.cpp
@@ -26,7 +26,6 @@
 */
 
 #include "gl/system/gl_system.h"
-#include "files.h"
 #include "m_swap.h"
 #include "v_video.h"
 #include "gl/gl_functions.h"
diff --git a/src/gl/shaders/gl_present3dRowshader.cpp b/src/gl/shaders/gl_present3dRowshader.cpp
index d8369a3b6..94dd7dc79 100644
--- a/src/gl/shaders/gl_present3dRowshader.cpp
+++ b/src/gl/shaders/gl_present3dRowshader.cpp
@@ -28,7 +28,6 @@
 */
 
 #include "gl/system/gl_system.h"
-#include "files.h"
 #include "m_swap.h"
 #include "v_video.h"
 #include "gl/gl_functions.h"
diff --git a/src/gl/shaders/gl_presentshader.cpp b/src/gl/shaders/gl_presentshader.cpp
index 15acc74fb..5fe040db9 100644
--- a/src/gl/shaders/gl_presentshader.cpp
+++ b/src/gl/shaders/gl_presentshader.cpp
@@ -26,7 +26,6 @@
 */
 
 #include "gl/system/gl_system.h"
-#include "files.h"
 #include "m_swap.h"
 #include "v_video.h"
 #include "gl/gl_functions.h"
diff --git a/src/gl/shaders/gl_shaderprogram.cpp b/src/gl/shaders/gl_shaderprogram.cpp
index 7a4690874..5327eeac0 100644
--- a/src/gl/shaders/gl_shaderprogram.cpp
+++ b/src/gl/shaders/gl_shaderprogram.cpp
@@ -26,7 +26,6 @@
 */
 
 #include "gl/system/gl_system.h"
-#include "files.h"
 #include "m_swap.h"
 #include "v_video.h"
 #include "gl/gl_functions.h"
diff --git a/src/gl/shaders/gl_tonemapshader.cpp b/src/gl/shaders/gl_tonemapshader.cpp
index 3db6db8ba..5045618be 100644
--- a/src/gl/shaders/gl_tonemapshader.cpp
+++ b/src/gl/shaders/gl_tonemapshader.cpp
@@ -26,7 +26,6 @@
 */
 
 #include "gl/system/gl_system.h"
-#include "files.h"
 #include "m_swap.h"
 #include "v_video.h"
 #include "gl/gl_functions.h"
diff --git a/src/gl/system/gl_framebuffer.cpp b/src/gl/system/gl_framebuffer.cpp
index c940e8b0d..e6f2833f8 100644
--- a/src/gl/system/gl_framebuffer.cpp
+++ b/src/gl/system/gl_framebuffer.cpp
@@ -27,7 +27,6 @@
 */
 
 #include "gl/system/gl_system.h"
-#include "files.h"
 #include "m_swap.h"
 #include "v_video.h"
 #include "doomstat.h"
diff --git a/src/gl/system/gl_swframebuffer.cpp b/src/gl/system/gl_swframebuffer.cpp
index 33c93c187..635f73fac 100644
--- a/src/gl/system/gl_swframebuffer.cpp
+++ b/src/gl/system/gl_swframebuffer.cpp
@@ -39,7 +39,6 @@
 */
 
 #include "gl/system/gl_system.h"
-#include "files.h"
 #include "m_swap.h"
 #include "v_video.h"
 #include "doomstat.h"
diff --git a/src/gl/system/gl_swwipe.cpp b/src/gl/system/gl_swwipe.cpp
index 03577773f..86fa11525 100644
--- a/src/gl/system/gl_swwipe.cpp
+++ b/src/gl/system/gl_swwipe.cpp
@@ -35,7 +35,6 @@
 // HEADER FILES ------------------------------------------------------------
 
 #include "gl/system/gl_system.h"
-#include "files.h"
 #include "m_swap.h"
 #include "v_video.h"
 #include "doomstat.h"
diff --git a/src/gl/system/gl_wipe.cpp b/src/gl/system/gl_wipe.cpp
index 88b9ef015..db03f99c1 100644
--- a/src/gl/system/gl_wipe.cpp
+++ b/src/gl/system/gl_wipe.cpp
@@ -25,7 +25,6 @@
 */
 
 #include "gl/system/gl_system.h"
-#include "files.h"
 #include "f_wipe.h"
 #include "m_random.h"
 #include "w_wad.h"
diff --git a/src/m_cheat.cpp b/src/m_cheat.cpp
index ace2c0c61..d395d0ad2 100644
--- a/src/m_cheat.cpp
+++ b/src/m_cheat.cpp
@@ -50,6 +50,7 @@
 #include "g_levellocals.h"
 #include "virtual.h"
 #include "events.h"
+#include "p_acs.h"
 
 // [RH] Actually handle the cheat. The cheat code in st_stuff.c now just
 // writes some bytes to the network data stream, and the network code
diff --git a/src/m_png.h b/src/m_png.h
index 2390059c1..70c45b710 100644
--- a/src/m_png.h
+++ b/src/m_png.h
@@ -36,8 +36,9 @@
 #include <stdio.h>
 #include "doomtype.h"
 #include "v_video.h"
-#include "files.h"
 
+class FileReader;
+class FileWriter;
 // PNG Writing --------------------------------------------------------------
 
 // Start writing an 8-bit palettized PNG file.
diff --git a/src/md5.cpp b/src/md5.cpp
index ae3cb53c0..aa4b506da 100644
--- a/src/md5.cpp
+++ b/src/md5.cpp
@@ -20,6 +20,7 @@
 #include "doomtype.h"
 #include "md5.h"
 #include "templates.h"
+#include "files.h"
 
 #ifdef __BIG_ENDIAN__
 void byteSwap(uint32_t *buf, unsigned words)
diff --git a/src/md5.h b/src/md5.h
index 1f2765378..a645919db 100644
--- a/src/md5.h
+++ b/src/md5.h
@@ -18,7 +18,7 @@
 #ifndef MD5_H
 #define MD5_H
 
-#include "files.h"
+class FileReader;
 
 struct MD5Context
 {
diff --git a/src/p_3dfloors.h b/src/p_3dfloors.h
index 2c0dbff64..4d52f550b 100644
--- a/src/p_3dfloors.h
+++ b/src/p_3dfloors.h
@@ -37,11 +37,7 @@ typedef enum
 } ffloortype_e;
 
 // This is for the purpose of Sector_SetContents:
-#ifdef _MSC_VER
-enum : unsigned int // MSVC is apparently the only compiler that supports this syntax
-#else
-enum
-#endif
+enum : unsigned int
 {
 	VC_EMPTY = 0, // Here's the original values of the color shifts in Vavoom, and in ARGB:
 	VC_WATER	 = 0x80825032,	// 130, 80, 50, 128		-> 80.82.50.32 (was 0x101080)
@@ -60,7 +56,8 @@ enum
 
 struct secplane_t;
 struct FDynamicColormap;
-
+struct line_t;
+struct sector_t;
 
 struct F3DFloor
 {
@@ -115,7 +112,7 @@ struct lightlist_t
 
 
 
-class player_s;
+class player_t;
 void P_PlayerOnSpecial3DFloor(player_t* player);
 
 bool P_CheckFor3DFloorHit(AActor * mo, double z);
diff --git a/src/p_acs.cpp b/src/p_acs.cpp
index 29230616f..c50e787d2 100644
--- a/src/p_acs.cpp
+++ b/src/p_acs.cpp
@@ -659,6 +659,134 @@ struct CallReturn
 	unsigned int EntryInstrCount;
 };
 
+
+class DLevelScript : public DObject
+{
+	DECLARE_CLASS(DLevelScript, DObject)
+	HAS_OBJECT_POINTERS
+public:
+
+
+	enum EScriptState
+	{
+		SCRIPT_Running,
+		SCRIPT_Suspended,
+		SCRIPT_Delayed,
+		SCRIPT_TagWait,
+		SCRIPT_PolyWait,
+		SCRIPT_ScriptWaitPre,
+		SCRIPT_ScriptWait,
+		SCRIPT_PleaseRemove,
+		SCRIPT_DivideBy0,
+		SCRIPT_ModulusBy0,
+	};
+
+	DLevelScript(AActor *who, line_t *where, int num, const ScriptPtr *code, FBehavior *module,
+		const int *args, int argcount, int flags);
+	~DLevelScript();
+
+	void Serialize(FSerializer &arc);
+	int RunScript();
+
+	inline void SetState(EScriptState newstate) { state = newstate; }
+	inline EScriptState GetState() { return state; }
+
+	DLevelScript *GetNext() const { return next; }
+
+	void MarkLocalVarStrings() const
+	{
+		GlobalACSStrings.MarkStringArray(&Localvars[0], Localvars.Size());
+	}
+	void LockLocalVarStrings() const
+	{
+		GlobalACSStrings.LockStringArray(&Localvars[0], Localvars.Size());
+	}
+	void UnlockLocalVarStrings() const
+	{
+		GlobalACSStrings.UnlockStringArray(&Localvars[0], Localvars.Size());
+	}
+
+protected:
+	DLevelScript	*next, *prev;
+	int				script;
+	TArray<int32_t>	Localvars;
+	int				*pc;
+	EScriptState	state;
+	int				statedata;
+	TObjPtr<AActor*>	activator;
+	line_t			*activationline;
+	bool			backSide;
+	FFont			*activefont;
+	int				hudwidth, hudheight;
+	int				ClipRectLeft, ClipRectTop, ClipRectWidth, ClipRectHeight;
+	int				WrapWidth;
+	bool			HandleAspect;
+	FBehavior	    *activeBehavior;
+	int				InModuleScriptNumber;
+
+	void Link();
+	void Unlink();
+	void PutLast();
+	void PutFirst();
+	static int Random(int min, int max);
+	static int ThingCount(int type, int stringid, int tid, int tag);
+	static void ChangeFlat(int tag, int name, bool floorOrCeiling);
+	static int CountPlayers();
+	static void SetLineTexture(int lineid, int side, int position, int name);
+	static int DoSpawn(int type, const DVector3 &pos, int tid, DAngle angle, bool force);
+	static int DoSpawn(int type, int x, int y, int z, int tid, int angle, bool force);
+	static bool DoCheckActorTexture(int tid, AActor *activator, int string, bool floor);
+	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, int32_t *args);
+
+	void DoFadeTo(int r, int g, int b, int a, int time);
+	void DoFadeRange(int r1, int g1, int b1, int a1,
+		int r2, int g2, int b2, int a2, int time);
+	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);
+	int CheckActorProperty(int tid, int property, int value);
+	int GetPlayerInput(int playernum, int inputnum);
+
+	int LineFromID(int id);
+	int SideFromID(int id, int side);
+
+private:
+	DLevelScript();
+
+	friend class DACSThinker;
+};
+
+class DACSThinker : public DThinker
+{
+	DECLARE_CLASS(DACSThinker, DThinker)
+	HAS_OBJECT_POINTERS
+public:
+	DACSThinker();
+	~DACSThinker();
+
+	void Serialize(FSerializer &arc);
+	void Tick();
+
+	typedef TMap<int, DLevelScript *> ScriptMap;
+	ScriptMap RunningScripts;	// Array of all synchronous scripts
+	static TObjPtr<DACSThinker*> ActiveThinker;
+
+	void DumpScriptStatus();
+	void StopScriptsFor(AActor *actor);
+
+private:
+	DLevelScript *LastScript;
+	DLevelScript *Scripts;				// List of all running scripts
+
+	friend class DLevelScript;
+	friend class FBehavior;
+};
+
+
 static DLevelScript *P_GetScriptGoing (AActor *who, line_t *where, int num, const ScriptPtr *code, FBehavior *module,
 	const int *args, int argcount, int flags);
 
@@ -10863,6 +10991,11 @@ CCMD(acsprofile)
 	ShowProfileData(FuncProfiles, limit, sorter, true);
 }
 
+void MarkACSThinker()
+{
+	GC::Mark(DACSThinker::ActiveThinker);
+}
+
 ADD_STAT(ACS)
 {
 	return FStringf("ACS time: %f ms", ACSTime.TimeMS());
diff --git a/src/p_acs.h b/src/p_acs.h
index 4943ef401..178a6ecce 100644
--- a/src/p_acs.h
+++ b/src/p_acs.h
@@ -35,8 +35,6 @@
 #ifndef __P_ACS_H__
 #define __P_ACS_H__
 
-#include "dobject.h"
-#include "dthinker.h"
 #include "doomtype.h"
 
 #define LOCAL_SIZE				20
@@ -385,147 +383,4 @@ private:
 	friend void ArrangeFunctionProfiles(TArray<ProfileCollector> &profiles);
 };
 
-class DLevelScript : public DObject
-{
-	DECLARE_CLASS (DLevelScript, DObject)
-	HAS_OBJECT_POINTERS
-public:
-
-
-	enum EScriptState
-	{
-		SCRIPT_Running,
-		SCRIPT_Suspended,
-		SCRIPT_Delayed,
-		SCRIPT_TagWait,
-		SCRIPT_PolyWait,
-		SCRIPT_ScriptWaitPre,
-		SCRIPT_ScriptWait,
-		SCRIPT_PleaseRemove,
-		SCRIPT_DivideBy0,
-		SCRIPT_ModulusBy0,
-	};
-
-	DLevelScript (AActor *who, line_t *where, int num, const ScriptPtr *code, FBehavior *module,
-		const int *args, int argcount, int flags);
-	~DLevelScript ();
-
-	void Serialize(FSerializer &arc);
-	int RunScript ();
-
-	inline void SetState (EScriptState newstate) { state = newstate; }
-	inline EScriptState GetState () { return state; }
-
-	DLevelScript *GetNext() const { return next; }
-
-	void MarkLocalVarStrings() const
-	{
-		GlobalACSStrings.MarkStringArray(&Localvars[0], Localvars.Size());
-	}
-	void LockLocalVarStrings() const
-	{
-		GlobalACSStrings.LockStringArray(&Localvars[0], Localvars.Size());
-	}
-	void UnlockLocalVarStrings() const
-	{
-		GlobalACSStrings.UnlockStringArray(&Localvars[0], Localvars.Size());
-	}
-
-protected:
-	DLevelScript	*next, *prev;
-	int				script;
-	TArray<int32_t>	Localvars;
-	int				*pc;
-	EScriptState	state;
-	int				statedata;
-	TObjPtr<AActor*>	activator;
-	line_t			*activationline;
-	bool			backSide;
-	FFont			*activefont;
-	int				hudwidth, hudheight;
-	int				ClipRectLeft, ClipRectTop, ClipRectWidth, ClipRectHeight;
-	int				WrapWidth;
-	bool			HandleAspect;
-	FBehavior	    *activeBehavior;
-	int				InModuleScriptNumber;
-
-	void Link ();
-	void Unlink ();
-	void PutLast ();
-	void PutFirst ();
-	static int Random (int min, int max);
-	static int ThingCount (int type, int stringid, int tid, int tag);
-	static void ChangeFlat (int tag, int name, bool floorOrCeiling);
-	static int CountPlayers ();
-	static void SetLineTexture (int lineid, int side, int position, int name);
-	static int DoSpawn (int type, const DVector3 &pos, int tid, DAngle angle, bool force);
-	static int DoSpawn(int type, int x, int y, int z, int tid, int angle, bool force);
-	static bool DoCheckActorTexture(int tid, AActor *activator, int string, bool floor);
-	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, int32_t *args);
-
-	void DoFadeTo (int r, int g, int b, int a, int time);
-	void DoFadeRange (int r1, int g1, int b1, int a1,
-		int r2, int g2, int b2, int a2, int time);
-	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);
-	int CheckActorProperty (int tid, int property, int value);
-	int GetPlayerInput (int playernum, int inputnum);
-
-	int LineFromID(int id);
-	int SideFromID(int id, int side);
-
-private:
-	DLevelScript ();
-
-	friend class DACSThinker;
-};
-
-class DACSThinker : public DThinker
-{
-	DECLARE_CLASS (DACSThinker, DThinker)
-	HAS_OBJECT_POINTERS
-public:
-	DACSThinker ();
-	~DACSThinker ();
-
-	void Serialize(FSerializer &arc);
-	void Tick ();
-
-	typedef TMap<int, DLevelScript *> ScriptMap;
-	ScriptMap RunningScripts;	// Array of all synchronous scripts
-	static TObjPtr<DACSThinker*> ActiveThinker;
-
-	void DumpScriptStatus();
-	void StopScriptsFor (AActor *actor);
-
-private:
-	DLevelScript *LastScript;
-	DLevelScript *Scripts;				// List of all running scripts
-
-	friend class DLevelScript;
-	friend class FBehavior;
-};
-
-// The structure used to control scripts between maps
-struct acsdefered_t
-{
-	enum EType
-	{
-		defexecute,
-		defexealways,
-		defsuspend,
-		defterminate
-	} type;
-	int script;
-	int args[3];
-	int playernum;
-};
-
-FSerializer &Serialize(FSerializer &arc, const char *key, acsdefered_t &defer, acsdefered_t *def);
-
 #endif //__P_ACS_H__
diff --git a/src/polyrenderer/drawers/poly_buffer.h b/src/polyrenderer/drawers/poly_buffer.h
index 4454f72fd..a135722fd 100644
--- a/src/polyrenderer/drawers/poly_buffer.h
+++ b/src/polyrenderer/drawers/poly_buffer.h
@@ -22,6 +22,8 @@
 
 #pragma once
 
+#include <vector>
+
 struct TriVertex;
 
 class PolySubsectorGBuffer
diff --git a/src/posix/cocoa/i_system.mm b/src/posix/cocoa/i_system.mm
index f36caca24..a9cb70809 100644
--- a/src/posix/cocoa/i_system.mm
+++ b/src/posix/cocoa/i_system.mm
@@ -38,7 +38,7 @@
 #include <sys/stat.h>
 #include <sys/sysctl.h>
 
-#include "d_ticcmd.h"
+#include "d_protocol.h"
 #include "doomdef.h"
 #include "doomerrors.h"
 #include "doomstat.h"
diff --git a/src/r_data/renderstyle.h b/src/r_data/renderstyle.h
index 364cf579e..ebc1bd53f 100644
--- a/src/r_data/renderstyle.h
+++ b/src/r_data/renderstyle.h
@@ -1,6 +1,4 @@
-#ifndef __R_BLEND_H
-#define __R_BLEND_H
-
+#pragma once
 /*
 ** r_blend.h
 ** Constants and types for specifying texture blending.
@@ -162,4 +160,3 @@ inline FRenderStyle &FRenderStyle::operator= (ERenderStyle legacy)
 	return *this;
 }
 
-#endif
diff --git a/src/s_sound.cpp b/src/s_sound.cpp
index 22f81a529..8e5ac7349 100644
--- a/src/s_sound.cpp
+++ b/src/s_sound.cpp
@@ -491,14 +491,14 @@ void S_PrecacheLevel ()
 				actor->MarkPrecacheSounds();
 			}
 		}
-		for (auto i : gameinfo.PrecachedSounds)
+		for (auto snd : gameinfo.PrecachedSounds)
 		{
-			level.info->PrecacheSounds[i].MarkUsed();
+			FSoundID(snd).MarkUsed();
 		}
 		// Precache all extra sounds requested by this map.
-		for (i = 0; i < level.info->PrecacheSounds.Size(); ++i)
+		for (auto snd : level.info->PrecacheSounds)
 		{
-			level.info->PrecacheSounds[i].MarkUsed();
+			FSoundID(snd).MarkUsed();
 		}
 		// Don't unload sounds that are playing right now.
 		for (FSoundChan *chan = Channels; chan != NULL; chan = chan->NextChan)
diff --git a/src/scripting/backend/scopebarrier.h b/src/scripting/backend/scopebarrier.h
index da0bc6d1d..fdcfedfba 100644
--- a/src/scripting/backend/scopebarrier.h
+++ b/src/scripting/backend/scopebarrier.h
@@ -2,6 +2,9 @@
 
 #include "zstring.h"
 
+class PClass;
+class VMFunction;
+
 //
 // [ZZ] this really should be in codegen.h, but vmexec needs to access it
 struct FScopeBarrier
diff --git a/src/scripting/thingdef_data.cpp b/src/scripting/thingdef_data.cpp
index a09134d58..c90cc17e8 100644
--- a/src/scripting/thingdef_data.cpp
+++ b/src/scripting/thingdef_data.cpp
@@ -50,7 +50,6 @@
 #include "zstring.h"
 #include "d_event.h"
 #include "g_levellocals.h"
-#include "vm.h"
 #include "p_checkposition.h"
 #include "r_sky.h"
 #include "v_font.h"
diff --git a/src/scripting/vm/vm.h b/src/scripting/vm/vm.h
index 3a4ffb02c..8a26a7d3f 100644
--- a/src/scripting/vm/vm.h
+++ b/src/scripting/vm/vm.h
@@ -844,11 +844,6 @@ struct VMRegisters
 	VMValue *param;
 };
 
-struct VMException : public DObject
-{
-	DECLARE_CLASS(VMException, DObject);
-};
-
 union FVoidObj
 {
 	DObject *o;
diff --git a/src/tarray.h b/src/tarray.h
index fe0d8c1e2..d6962816c 100644
--- a/src/tarray.h
+++ b/src/tarray.h
@@ -1,3 +1,4 @@
+#pragma once
 /*
 ** tarray.h
 ** Templated, automatically resizing array
@@ -32,8 +33,6 @@
 **
 */
 
-#ifndef __TARRAY_H__
-#define __TARRAY_H__
 
 #include <stdlib.h>
 #include <assert.h>
@@ -1250,4 +1249,3 @@ protected:
 	hash_t Position;
 };
 
-#endif //__TARRAY_H__
diff --git a/src/v_palette.cpp b/src/v_palette.cpp
index f816c9728..1c13446a8 100644
--- a/src/v_palette.cpp
+++ b/src/v_palette.cpp
@@ -32,6 +32,8 @@
 **
 */
 
+#include "g_level.h"
+
 #include <stddef.h>
 #include <string.h>
 #include <math.h>
@@ -50,7 +52,6 @@
 #include "w_wad.h"
 #include "i_video.h"
 #include "c_dispatch.h"
-#include "g_level.h"
 #include "st_stuff.h"
 #include "gi.h"
 #include "x86.h"
diff --git a/src/zstring.h b/src/zstring.h
index e486a0e8b..4de4a2ba0 100644
--- a/src/zstring.h
+++ b/src/zstring.h
@@ -1,3 +1,4 @@
+#pragma once
 /*
 ** zstring.h
 **
@@ -31,8 +32,6 @@
 **
 */
 
-#ifndef ZSTRING_H
-#define ZSTRING_H
 
 #include <stdio.h>
 #include <stdarg.h>
@@ -450,4 +449,3 @@ template<> struct THashTraits<FString>
 	int Compare(const FString &left, const FString &right) { return left.Compare(right); }
 };
 
-#endif