diff --git a/src/d_main.cpp b/src/d_main.cpp
index 842b1e9f4..556664662 100644
--- a/src/d_main.cpp
+++ b/src/d_main.cpp
@@ -703,7 +703,7 @@ CUSTOM_CVAR(Int, compatmode, 0, CVAR_ARCHIVE|CVAR_NOINITCALL)
 	case 5: // MBF compat mode
 		v = COMPATF_TRACE | COMPATF_SOUNDTARGET | COMPATF_BOOMSCROLL | COMPATF_MISSILECLIP | COMPATF_MUSHROOM |
 			COMPATF_MBFMONSTERMOVE | COMPATF_NOBLOCKFRIENDS | COMPATF_MASKEDMIDTEX;
-		w = COMPATF2_EXPLODE1;
+		w = COMPATF2_EXPLODE1 | COMPATF2_AVOID_HAZARDS | COMPATF2_STAYONLIFT;
 		break;
 
 	case 6:	// Boom with some added settings to reenable some 'broken' behavior
@@ -716,7 +716,7 @@ CUSTOM_CVAR(Int, compatmode, 0, CVAR_ARCHIVE|CVAR_NOINITCALL)
 		v = COMPATF_CORPSEGIBS | COMPATF_NOBLOCKFRIENDS | COMPATF_MBFMONSTERMOVE | COMPATF_INVISIBILITY |
 			COMPATF_NOTOSSDROPS | COMPATF_MUSHROOM | COMPATF_NO_PASSMOBJ | COMPATF_BOOMSCROLL | COMPATF_WALLRUN |
 			COMPATF_TRACE | COMPATF_HITSCAN | COMPATF_MISSILECLIP | COMPATF_MASKEDMIDTEX | COMPATF_SOUNDTARGET;
-		w = COMPATF2_POINTONLINE | COMPATF2_EXPLODE1 | COMPATF2_EXPLODE2;
+		w = COMPATF2_POINTONLINE | COMPATF2_EXPLODE1 | COMPATF2_EXPLODE2 | COMPATF2_AVOID_HAZARDS | COMPATF2_STAYONLIFT;
 		break;
 	}
 	compatflags = v;
@@ -766,6 +766,8 @@ CVAR (Flag, compat_checkswitchrange,	compatflags2, COMPATF2_CHECKSWITCHRANGE);
 CVAR (Flag, compat_explode1,			compatflags2, COMPATF2_EXPLODE1);
 CVAR (Flag, compat_explode2,			compatflags2, COMPATF2_EXPLODE2);
 CVAR (Flag, compat_railing,				compatflags2, COMPATF2_RAILING);
+CVAR (Flag, compat_avoidhazard,			compatflags2, COMPATF2_AVOID_HAZARDS);
+CVAR (Flag, compat_stayonlift,			compatflags2, COMPATF2_STAYONLIFT);
 
 CVAR(Bool, vid_activeinbackground, false, CVAR_ARCHIVE | CVAR_GLOBALCONFIG)
 
diff --git a/src/doomdef.h b/src/doomdef.h
index 1adf81d7d..05e7ebb95 100644
--- a/src/doomdef.h
+++ b/src/doomdef.h
@@ -222,6 +222,9 @@ enum : unsigned int
 	COMPATF2_EXPLODE2		= 1 << 9,	// Use original explosion code throughout.
 	COMPATF2_RAILING		= 1 << 10,	// Bugged Strife railings.
 	COMPATF2_SCRIPTWAIT		= 1 << 11,	// Use old scriptwait implementation where it doesn't wait on a non-running script.
+	COMPATF2_AVOID_HAZARDS	= 1 << 12,	// another MBF thing.
+	COMPATF2_STAYONLIFT		= 1 << 13,	// yet another MBF thing.
+
 };
 
 // Emulate old bugs for select maps. These are not exposed by a cvar
diff --git a/src/gamedata/g_mapinfo.cpp b/src/gamedata/g_mapinfo.cpp
index 3b8c5ca3b..3b823c59e 100644
--- a/src/gamedata/g_mapinfo.cpp
+++ b/src/gamedata/g_mapinfo.cpp
@@ -1663,7 +1663,6 @@ MapFlagHandlers[] =
 	{ "enableskyboxao",					MITYPE_SETFLAG3,	LEVEL3_SKYBOXAO, 0 },
 	{ "disableskyboxao",				MITYPE_CLRFLAG3,	LEVEL3_SKYBOXAO, 0 },
 	{ "avoidmelee",						MITYPE_SETFLAG3,	LEVEL3_AVOIDMELEE, 0 },
-	{ "avoidhazards",					MITYPE_SETFLAG3,	LEVEL3_AVOID_HAZARDS, 0 },
 	{ "nobotnodes",						MITYPE_IGNORE,	0, 0 },		// Skulltag option: nobotnodes
 	{ "compat_shorttex",				MITYPE_COMPATFLAG, COMPATF_SHORTTEX, 0 },
 	{ "compat_stairs",					MITYPE_COMPATFLAG, COMPATF_STAIRINDEX, 0 },
@@ -1705,6 +1704,8 @@ MapFlagHandlers[] =
 	{ "compat_explode2",				MITYPE_COMPATFLAG, 0, COMPATF2_EXPLODE2 },
 	{ "compat_railing",					MITYPE_COMPATFLAG, 0, COMPATF2_RAILING },
 	{ "compat_scriptwait",				MITYPE_COMPATFLAG, 0, COMPATF2_SCRIPTWAIT },
+	{ "compat_avoidhazards",			MITYPE_COMPATFLAG, 0, COMPATF2_AVOID_HAZARDS },
+	{ "compat_stayonlift",				MITYPE_COMPATFLAG, 0, COMPATF2_STAYONLIFT },
 	{ "cd_start_track",					MITYPE_EATNEXT,	0, 0 },
 	{ "cd_end1_track",					MITYPE_EATNEXT,	0, 0 },
 	{ "cd_end2_track",					MITYPE_EATNEXT,	0, 0 },
diff --git a/src/gamedata/g_mapinfo.h b/src/gamedata/g_mapinfo.h
index ecb6ba0e6..9f7472854 100644
--- a/src/gamedata/g_mapinfo.h
+++ b/src/gamedata/g_mapinfo.h
@@ -260,7 +260,6 @@ enum ELevelFlags : unsigned int
 	LEVEL3_NOSHADOWMAP			= 0x00010000,	// disables shadowmaps for a given level.
 	LEVEL3_AVOIDMELEE			= 0x00020000,	// global flag needed for proper MBF support.
 	LEVEL3_NOJUMPDOWN			= 0x00040000,	// only for MBF21. Inverse of MBF's dog_jumping flag.
-	LEVEL3_AVOID_HAZARDS		= 0x00080000,	// another MBF thing.
 };
 
 
diff --git a/src/gamedata/r_defs.h b/src/gamedata/r_defs.h
index fa4a30227..d7fb686cf 100644
--- a/src/gamedata/r_defs.h
+++ b/src/gamedata/r_defs.h
@@ -485,6 +485,7 @@ enum
 	SECMF_HIDDEN			= 256,	// Do not draw on textured automap
 	SECMF_OVERLAPPING		= 512,	// floor and ceiling overlap and require special renderer action.
 	SECMF_NOSKYWALLS		= 1024,	// Do not draw "sky walls"
+	SECMF_LIFT				= 2048,	// For MBF monster AI
 };
 
 enum
diff --git a/src/maploader/specials.cpp b/src/maploader/specials.cpp
index 2024954f7..280eba279 100644
--- a/src/maploader/specials.cpp
+++ b/src/maploader/specials.cpp
@@ -787,6 +787,27 @@ void MapLoader::SpawnSpecials ()
 			SpawnLinePortal(&line);
 			break;
 
+			// partial support for MBF's stay-on-lift feature.
+			// Unlike MBF we cannot scan all lines for a proper special each time because it'd take too long.
+			// So instead, set the info here, but only for repeatable lifts to keep things simple. 
+			// This also cannot consider lifts triggered by scripts etc.
+		case Generic_Lift:
+			if (line.args[3] != 1) continue;
+		case Plat_DownWaitUpStay:
+		case Plat_DownWaitUpStayLip:
+		case Plat_UpWaitDownStay:
+		case Plat_UpNearestWaitDownStay:
+			if (line.flags & ML_REPEAT_SPECIAL)
+			{
+				auto it = Level->GetSectorTagIterator(line.args[0], &line);
+				int secno;
+				while ((secno = it.Next()) != -1)
+				{
+					Level->sectors[secno].MoreFlags |= SECMF_LIFT;
+				}
+			}
+			break;
+
 		// [RH] ZDoom Static_Init settings
 		case Static_Init:
 			switch (line.args[1])
diff --git a/src/playsim/actor.h b/src/playsim/actor.h
index 61b65b593..e604cbfeb 100644
--- a/src/playsim/actor.h
+++ b/src/playsim/actor.h
@@ -422,6 +422,7 @@ enum ActorFlag8
 	MF8_MAP07BOSS1		= 0x00400000,	// MBF21 boss death.
 	MF8_MAP07BOSS2		= 0x00800000,	// MBF21 boss death.
 	MF8_AVOIDHAZARDS	= 0x01000000,	// MBF AI enhancement.
+	MF8_STAYONLIFT		= 0x02000000,	// MBF AI enhancement.
 };
 
 // --- mobj.renderflags ---
diff --git a/src/playsim/p_enemy.cpp b/src/playsim/p_enemy.cpp
index 1432fa67d..b877bcd12 100644
--- a/src/playsim/p_enemy.cpp
+++ b/src/playsim/p_enemy.cpp
@@ -69,6 +69,7 @@ static FRandom pr_slook ("SlooK");
 static FRandom pr_dropoff ("Dropoff");
 static FRandom pr_defect ("Defect");
 static FRandom pr_avoidcrush("AvoidCrush");
+static FRandom pr_stayonlift("StayOnLift");
 
 static FRandom pr_skiptarget("SkipTarget");
 static FRandom pr_enemystrafe("EnemyStrafe");
@@ -409,6 +410,33 @@ int P_HitFriend(AActor * self)
 	return false;
 }
 
+/*
+ * P_IsOnLift
+ *
+ * killough 9/9/98:
+ *
+ * Returns true if the object is on a lift. Used for AI,
+ * since it may indicate the need for crowded conditions,
+ * or that a monster should stay on the lift for a while
+ * while it goes up or down.
+ */
+
+static bool P_IsOnLift(const AActor* actor)
+{
+	sector_t* sec = actor->Sector;
+
+	// Short-circuit: it's on a lift which is active.
+	DSectorEffect* e = sec->floordata;
+	if (e && e->IsKindOf(RUNTIME_CLASS(DPlat)))
+		return true;
+
+	// Check to see if it's in a sector which can be activated as a lift.
+	// This is a bit more restrictive than MBF as it only considers repeatable lifts moving from A->B->A and stop.
+	// Other types of movement are not easy to detect with the more complex map setup 
+	// and also do not really make sense in this context unless they are actually active
+	return !!(sec->MoreFlags & SECMF_LIFT);
+}
+
 /*
  * P_IsUnderDamage
  *
@@ -437,6 +465,20 @@ static int P_IsUnderDamage(AActor* actor)
 	return dir;
 }
 
+//
+// P_CheckTags
+// Checks if 2 sectors share the same primary activation tag
+//
+
+bool P_CheckTags(sector_t* sec1, sector_t* sec2)
+{
+	auto Level = sec1->Level;
+	if (!Level->SectorHasTags(sec1) || !Level->SectorHasTags(sec2)) return sec1 == sec2;
+	if (Level->GetFirstSectorTag(sec1) == Level->GetFirstSectorTag(sec2)) return true;
+	// todo: check secondary tags as well.
+	return false;
+}
+
 //
 // P_Move
 // Move in the current direction,
@@ -686,15 +728,12 @@ int P_SmartMove(AActor* actor)
 {
 	AActor* target = actor->target;
 	int on_lift = false, dropoff = false, under_damage;
-	bool monster_avoid_hazards = (actor->Level->flags3 & LEVEL3_AVOID_HAZARDS) || (actor->flags8 & MF8_AVOIDHAZARDS);
+	bool monster_avoid_hazards = (actor->Level->i_compatflags2 & COMPATF2_AVOID_HAZARDS) || (actor->flags8 & MF8_AVOIDHAZARDS);
 
-#if 0
 	  /* killough 9/12/98: Stay on a lift if target is on one */
-	on_lift = !comp[comp_staylift]
-		&& target && target->health > 0
-		&& target->subsector->sector->tag == actor->subsector->sector->tag &&
-		P_IsOnLift(actor);
-#endif
+	on_lift = ((actor->flags8 & MF8_STAYONLIFT) || (actor->Level->i_compatflags2 & COMPATF2_STAYONLIFT))
+		&& target && target->health > 0 && P_IsOnLift(actor)
+		&& P_CheckTags(target->Sector, actor->Sector);
 
 	under_damage = monster_avoid_hazards && P_IsUnderDamage(actor) != 0;//e6y
 
@@ -703,11 +742,9 @@ int P_SmartMove(AActor* actor)
 
 	// killough 9/9/98: avoid crushing ceilings or other damaging areas
 	if (
-#if 0
-		(on_lift && P_Random(pr_stayonlift) < 230 &&      // Stay on lift
+		(on_lift && pr_stayonlift() < 230 &&      // Stay on lift
 			!P_IsOnLift(actor))
 		||
-#endif
 		(monster_avoid_hazards && !under_damage &&	//e6y  // Get away from damage
 			(under_damage = P_IsUnderDamage(actor)) &&
 			(under_damage < 0 || pr_avoidcrush() < 200))