diff --git a/src/actor.h b/src/actor.h
index d3cba00411..21057d86c3 100644
--- a/src/actor.h
+++ b/src/actor.h
@@ -1008,6 +1008,7 @@ public:
 	bool SetState (FState *newstate, bool nofunction=false);
 	virtual bool UpdateWaterLevel (fixed_t oldz, bool splash=true);
 	bool isFast();
+	bool isSlow();
 	void SetIdle();
 	void ClearCounters();
 
diff --git a/src/g_level.h b/src/g_level.h
index c431b96956..4a84e6871f 100644
--- a/src/g_level.h
+++ b/src/g_level.h
@@ -554,6 +554,7 @@ enum ESkillProperty
 	SKILLP_NoPain,
 	SKILLP_ArmorFactor,
 	SKILLP_EasyKey,
+	SKILLP_SlowMonsters,
 };
 int G_SkillProperty(ESkillProperty prop);
 const char * G_SkillName();
@@ -568,6 +569,7 @@ struct FSkillInfo
 	fixed_t AmmoFactor, DoubleAmmoFactor, DropAmmoFactor;
 	fixed_t DamageFactor;
 	bool FastMonsters;
+	bool SlowMonsters;
 	bool DisableCheats;
 	bool AutoUseHealth;
 
diff --git a/src/g_skill.cpp b/src/g_skill.cpp
index 46b9a1702a..ddfdbb4cc1 100644
--- a/src/g_skill.cpp
+++ b/src/g_skill.cpp
@@ -64,6 +64,7 @@ void FMapInfoParser::ParseSkill ()
 	skill.DropAmmoFactor = -1;
 	skill.DamageFactor = FRACUNIT;
 	skill.FastMonsters = false;
+	skill.SlowMonsters = false;
 	skill.DisableCheats = false;
 	skill.EasyBossBrain = false;
 	skill.EasyKey = false;
@@ -118,6 +119,10 @@ void FMapInfoParser::ParseSkill ()
 		{
 			skill.FastMonsters = true;
 		}
+		else if (sc.Compare ("slowmonsters"))
+		{
+			skill.SlowMonsters = true;
+		}
 		else if (sc.Compare ("disablecheats"))
 		{
 			skill.DisableCheats = true;
@@ -336,6 +341,9 @@ int G_SkillProperty(ESkillProperty prop)
 		case SKILLP_FastMonsters:
 			return AllSkills[gameskill].FastMonsters  || (dmflags & DF_FAST_MONSTERS);
 
+		case SKILLP_SlowMonsters:
+			return AllSkills[gameskill].SlowMonsters;
+
 		case SKILLP_Respawn:
 			if (dmflags & DF_MONSTERS_RESPAWN && AllSkills[gameskill].RespawnCounter==0) 
 				return TICRATE * gameinfo.defaultrespawntime;
@@ -433,6 +441,7 @@ FSkillInfo &FSkillInfo::operator=(const FSkillInfo &other)
 	DropAmmoFactor = other.DropAmmoFactor;
 	DamageFactor = other.DamageFactor;
 	FastMonsters = other.FastMonsters;
+	SlowMonsters = other.SlowMonsters;
 	DisableCheats = other.DisableCheats;
 	AutoUseHealth = other.AutoUseHealth;
 	EasyBossBrain = other.EasyBossBrain;
diff --git a/src/info.h b/src/info.h
index 9a316c78de..51c4bd629d 100644
--- a/src/info.h
+++ b/src/info.h
@@ -77,6 +77,7 @@ struct FState
 	BYTE		Fast:1;
 	BYTE		NoDelay:1;		// Spawn states executes its action normally
 	BYTE		CanRaise:1;		// Allows a monster to be resurrected without waiting for an infinate frame
+	BYTE		Slow:1;			// Inverse of fast
 	int			ParameterIndex;
 
 	inline int GetFrame() const
diff --git a/src/p_mobj.cpp b/src/p_mobj.cpp
index 291f51a946..f82cf9bce4 100644
--- a/src/p_mobj.cpp
+++ b/src/p_mobj.cpp
@@ -405,7 +405,7 @@ bool AActor::InStateSequence(FState * newstate, FState * basestate)
 //
 // Get the actual duration of the next state
 // We are using a state flag now to indicate a state that should be
-// accelerated in Fast mode.
+// accelerated in Fast mode or slowed in Slow mode.
 //
 //==========================================================================
 
@@ -416,6 +416,10 @@ int AActor::GetTics(FState * newstate)
 	{
 		return tics - (tics>>1);
 	}
+	else if (isSlow() && newstate->Slow)
+	{
+		return tics<<1;
+	}
 	return tics;
 }
 
@@ -4082,6 +4086,11 @@ bool AActor::isFast()
 	return !!G_SkillProperty(SKILLP_FastMonsters);
 }
 
+bool AActor::isSlow()
+{
+	return !!G_SkillProperty(SKILLP_SlowMonsters);
+}
+
 void AActor::Activate (AActor *activator)
 {
 	if ((flags3 & MF3_ISMONSTER) && (health > 0 || (flags & MF_ICECORPSE)))
diff --git a/src/thingdef/thingdef_states.cpp b/src/thingdef/thingdef_states.cpp
index 5cc2de1c03..6a28e54cdf 100644
--- a/src/thingdef/thingdef_states.cpp
+++ b/src/thingdef/thingdef_states.cpp
@@ -275,6 +275,11 @@ do_stop:
 					state.Fast = true;
 					continue;
 				}
+				if (sc.Compare("SLOW")) 
+				{
+					state.Slow = true;
+					continue;
+				}
 				if (sc.Compare("NODELAY"))
 				{
 					if (bag.statedef.GetStateLabelIndex(NAME_Spawn) == bag.statedef.GetStateCount())