I know this isn't my branch, but found several reference haemmoragers and figured it'd be appropriate to commit here.

src/hardware/hw_light.c

@@ -804,6 +804,14 @@ void HWR_WallLighting(FOutVector *wlVerts)
 		FSurfaceInfo    Surf;
 		float           dist_p2d, d[4], s;
 
+		if (!dynlights->mo[j])
+			continue;
+		if (P_MobjWasRemoved(dynlights->mo[j]))
+		{
+			P_SetTarget(&dynlights->mo[j], NULL);
+			continue;
+		}
+
 		// check bounding box first
 		if (SphereTouchBBox3D(&wlVerts[2], &wlVerts[0], &LIGHT_POS(j), DL_RADIUS(j))==false)
 			continue;
@@ -854,8 +862,6 @@ void HWR_WallLighting(FOutVector *wlVerts)
 #ifdef DL_HIGH_QUALITY
 		Surf.FlatColor.s.alpha = (UINT8)((1-dist_p2d/DL_SQRRADIUS(j))*Surf.FlatColor.s.alpha);
 #endif
-		if (!dynlights->mo[j]->state)
-			return;
 		// next state is null so fade out with alpha
 		if (dynlights->mo[j]->state->nextstate == S_NULL)
 			Surf.FlatColor.s.alpha = (UINT8)(((float)dynlights->mo[j]->tics/(float)dynlights->mo[j]->state->tics)*Surf.FlatColor.s.alpha);
@@ -886,6 +892,14 @@ void HWR_PlaneLighting(FOutVector *clVerts, int nrClipVerts)
 		FSurfaceInfo    Surf;
 		float           dist_p2d, s;
 
+		if (!dynlights->mo[j])
+			continue;
+		if (P_MobjWasRemoved(dynlights->mo[j]))
+		{
+			P_SetTarget(&dynlights->mo[j], NULL);
+			continue;
+		}
+
 		// BP: The kickass Optimization: check if light touch bounding box
 		if (SphereTouchBBox3D(&p1, &p2, &dynlights->position[j], DL_RADIUS(j))==false)
 			continue;
@@ -917,8 +931,6 @@ void HWR_PlaneLighting(FOutVector *clVerts, int nrClipVerts)
 #ifdef DL_HIGH_QUALITY
 		Surf.FlatColor.s.alpha = (unsigned char)((1 - dist_p2d/DL_SQRRADIUS(j))*Surf.FlatColor.s.alpha);
 #endif
-		if (!dynlights->mo[j]->state)
-			return;
 		// next state is null so fade out with alpha
 		if ((dynlights->mo[j]->state->nextstate == S_NULL))
 			Surf.FlatColor.s.alpha = (unsigned char)(((float)dynlights->mo[j]->tics/(float)dynlights->mo[j]->state->tics)*Surf.FlatColor.s.alpha);
@@ -1110,7 +1122,8 @@ void HWR_DrawCoronas(void)
 // --------------------------------------------------------------------------
 void HWR_ResetLights(void)
 {
-	dynlights->nb = 0;
+	while (dynlights->nb)
+		P_SetTarget(&dynlights->mo[--dynlights->nb], NULL);
 }
 
 // --------------------------------------------------------------------------
@@ -1145,9 +1158,7 @@ void HWR_DL_AddLight(gr_vissprite_t *spr, GLPatch_t *patch)
 	p_lspr = t_lspr[spr->mobj->sprite];
 	if ((p_lspr->type&DYNLIGHT_SPR)
 	  && ((p_lspr->type != LIGHT_SPR) || cv_grstaticlighting.value)
-	  && (dynlights->nb < DL_MAX_LIGHT)
+	  && (dynlights->nb < DL_MAX_LIGHT))
-
-	  && spr->mobj->state)
 	{
 		LIGHT_POS(dynlights->nb).x = FIXED_TO_FLOAT(spr->mobj->x);
 		LIGHT_POS(dynlights->nb).y = FIXED_TO_FLOAT(spr->mobj->z)+FIXED_TO_FLOAT(spr->mobj->height>>1)+p_lspr->light_yoffset;
@@ -1380,7 +1391,7 @@ void HWR_CreateStaticLightmaps(int bspnum)
 #ifdef STATICLIGHT
 	CONS_Debug(DBG_RENDER, "HWR_CreateStaticLightmaps\n");
 
-	dynlights->nb = 0;
+	HWR_ResetLights();
 
 	// First: Searching for lights
 	// BP: if i was you, I will make it in create mobj since mobj can be create
@@ -1392,7 +1403,7 @@ void HWR_CreateStaticLightmaps(int bspnum)
 	validcount++; // to be sure
 	HWR_ComputeLightMapsInBSPNode(bspnum, NULL);
 
-	dynlights->nb = 0;
+	HWR_ResetLights();
 #else
 	(void)bspnum;
 #endif

src/lua_blockmaplib.c

@@ -54,10 +54,12 @@ static UINT8 lib_searchBlockmap_Objects(lua_State *L, INT32 x, INT32 y, mobj_t *
 				CONS_Alert(CONS_WARNING,"%s\n",lua_tostring(gL, -1));
 			lua_pop(gL, 1);
 			blockfuncerror = true;
+			P_SetTarget(&bnext, NULL);
 			return 0; // *shrugs*
 		}
 		if (!lua_isnil(gL, -1))
 		{ // if nil, continue
+			P_SetTarget(&bnext, NULL);
 			if (lua_toboolean(gL, -1))
 				return 2; // stop whole search
 			else

src/lua_mobjlib.c

@@ -274,10 +274,19 @@ static int mobj_get(lua_State *L)
 		// bprev -- same deal as sprev above, but for the blockmap.
 		return UNIMPLEMENTED;
 	case mobj_hnext:
+		if (mo->hnext && P_MobjWasRemoved(mo->hnext))
+		{ // don't put invalid mobj back into Lua.
+			P_SetTarget(&mo->hnext, NULL);
+			return 0;
+		}
 		LUA_PushUserdata(L, mo->hnext, META_MOBJ);
 		break;
 	case mobj_hprev:
-		// implimented differently from sprev and bprev because SSNTails.
+		if (mo->hprev && P_MobjWasRemoved(mo->hprev))
+		{ // don't put invalid mobj back into Lua.
+			P_SetTarget(&mo->hprev, NULL);
+			return 0;
+		}
 		LUA_PushUserdata(L, mo->hprev, META_MOBJ);
 		break;
 	case mobj_type:

src/lua_playerlib.c

@@ -476,7 +476,12 @@ static int player_set(lua_State *L)
 	else if (fastcmp(field,"followitem"))
 		plr->followitem = luaL_checkinteger(L, 3);
 	else if (fastcmp(field,"followmobj"))
-		P_SetTarget(&plr->followmobj, *((mobj_t **)luaL_checkudata(L, 3, META_MOBJ)));
+	{
+		mobj_t *mo = NULL;
+		if (!lua_isnil(L, 3))
+			mo = *((mobj_t **)luaL_checkudata(L, 3, META_MOBJ));
+		P_SetTarget(&plr->followmobj, mo);
+	}
 	else if (fastcmp(field,"actionspd"))
 		plr->actionspd = (INT32)luaL_checkinteger(L, 3);
 	else if (fastcmp(field,"mindash"))
@@ -560,9 +565,19 @@ static int player_set(lua_State *L)
 	else if (fastcmp(field,"old_angle_pos"))
 		plr->old_angle_pos = luaL_checkangle(L, 3);
 	else if (fastcmp(field,"axis1"))
-		P_SetTarget(&plr->axis1, *((mobj_t **)luaL_checkudata(L, 3, META_MOBJ)));
+	{
+		mobj_t *mo = NULL;
+		if (!lua_isnil(L, 3))
+			mo = *((mobj_t **)luaL_checkudata(L, 3, META_MOBJ));
+		P_SetTarget(&plr->axis1, mo);
+	}
 	else if (fastcmp(field,"axis2"))
-		P_SetTarget(&plr->axis2, *((mobj_t **)luaL_checkudata(L, 3, META_MOBJ)));
+	{
+		mobj_t *mo = NULL;
+		if (!lua_isnil(L, 3))
+			mo = *((mobj_t **)luaL_checkudata(L, 3, META_MOBJ));
+		P_SetTarget(&plr->axis2, mo);
+	}
 	else if (fastcmp(field,"bumpertime"))
 		plr->bumpertime = (tic_t)luaL_checkinteger(L, 3);
 	else if (fastcmp(field,"flyangle"))

src/p_maputl.c

@@ -1093,7 +1093,10 @@ boolean P_BlockThingsIterator(INT32 x, INT32 y, boolean (*func)(mobj_t *))
 	{
 		P_SetTarget(&bnext, mobj->bnext); // We want to note our reference to bnext here incase it is MF_NOTHINK and gets removed!
 		if (!func(mobj))
+		{
+			P_SetTarget(&bnext, NULL);
 			return false;
+		}
 		if (P_MobjWasRemoved(tmthing) // func just popped our tmthing, cannot continue.
 		|| (bnext && P_MobjWasRemoved(bnext))) // func just broke blockmap chain, cannot continue.
 		{

src/p_user.c

@@ -3655,7 +3655,8 @@ static void P_DoTeeter(player_t *player)
 		if (teeter) // only bother with objects as a last resort if you were already teetering
 		{
 			mobj_t *oldtmthing = tmthing;
-			tmthing = teeterer = player->mo;
+			teeterer = player->mo;
+			P_SetTarget(&tmthing, teeterer);
 			teeterxl = teeterxh = player->mo->x;
 			teeteryl = teeteryh = player->mo->y;
 			couldteeter = false;
@@ -3669,7 +3670,7 @@ static void P_DoTeeter(player_t *player)
 				}
 teeterdone:
 			teeter = solidteeter;
-			tmthing = oldtmthing; // restore old tmthing, goodness knows what the game does with this before mobj thinkers
+			P_SetTarget(&tmthing, oldtmthing); // restore old tmthing, goodness knows what the game does with this before mobj thinkers
 		}
 	}
 	if (teeter)