Revert "Removes some unnecessary global variables (#16353)" (#17170)

code/game/objects/effects/decals/Cleanable/humans.dm

@@ -1,5 +1,7 @@
 #define DRYING_TIME 5 * 60 * 10 //for 1 unit of depth in puddle (amount var)
 
+GLOBAL_LIST_EMPTY(splatter_cache)
+
 /obj/effect/decal/cleanable/blood
 	name = "blood"
 	var/dryname = "dried blood"

code/game/objects/obj_defense.dm

@@ -163,13 +163,15 @@
 
 ///// ACID
 
+GLOBAL_DATUM_INIT(acid_overlay, /mutable_appearance, mutable_appearance('icons/effects/effects.dmi', "acid"))
+
 ///the obj's reaction when touched by acid
 /obj/acid_act(acidpwr, acid_volume)
 	if(!(resistance_flags & UNACIDABLE) && acid_volume)
 
 		if(!acid_level)
 			SSacid.processing[src] = src
-			add_overlay(SSacid.acid_overlay, TRUE)
+			add_overlay(GLOB.acid_overlay, TRUE)
 		var/acid_cap = acidpwr * 300 //so we cannot use huge amounts of weak acids to do as well as strong acids.
 		if(acid_level < acid_cap)
 			acid_level = min(acid_level + acidpwr * acid_volume, acid_cap)