diff --git a/mods/ENTITIES/mcl_mobs/spawning.lua b/mods/ENTITIES/mcl_mobs/spawning.lua
index ef64843a8..ecb2318f2 100644
--- a/mods/ENTITIES/mcl_mobs/spawning.lua
+++ b/mods/ENTITIES/mcl_mobs/spawning.lua
@@ -25,6 +25,7 @@ local math_ceil      = math.ceil
 local math_cos       = math.cos
 local math_sin       = math.sin
 local math_sqrt      = math.sqrt
+local math_abs       = math.abs
 
 local vector_distance = vector.distance
 local vector_new      = vector.new
@@ -286,11 +287,7 @@ local function count_mobs_total(mob_type)
 end
 
 local function count_mobs_add_entry (mobs_list, mob_cat)
-	if mobs_list[mob_cat] then
-		mobs_list[mob_cat] = mobs_list[mob_cat] + 1
-	else
-		mobs_list[mob_cat] = 1
-	end
+	mobs_list[mob_cat] = (mobs_list[mob_cat] or 0) + 1
 end
 
 --categorise_by can be name or type or spawn_class
@@ -616,14 +613,14 @@ local function get_next_mob_spawn_pos(pos)
 	xoff, yoff, zoff = xoff * dd, yoff * dd, zoff * dd
 	local goal_pos = vector.offset(pos, xoff, yoff, zoff)
 
-	if not ( math.abs(goal_pos.x) <= SPAWN_MAPGEN_LIMIT and math.abs(goal_pos.y) <= SPAWN_MAPGEN_LIMIT and math.abs(goal_pos.z) <= SPAWN_MAPGEN_LIMIT ) then
+	if not (math_abs(goal_pos.x) <= SPAWN_MAPGEN_LIMIT and math_abs(goal_pos.y) <= SPAWN_MAPGEN_LIMIT and math_abs(goal_pos.z) <= SPAWN_MAPGEN_LIMIT) then
 		mcl_log("Pos outside mapgen limits: " .. minetest.pos_to_string(goal_pos))
 		return nil
 	end
 
 	-- Calculate upper/lower y limits
 	local d2 = xoff*xoff + zoff*zoff -- squared distance in x,z plane only
-	local y1 = math_sqrt( MOB_SPAWN_ZONE_OUTER_SQ - d2 ) -- absolue value of distance to outer sphere
+	local y1 = math_sqrt(MOB_SPAWN_ZONE_OUTER_SQ - d2) -- absolue value of distance to outer sphere
 
 	local y_min, y_max
 	if d2 >= MOB_SPAWN_ZONE_INNER_SQ then
@@ -632,7 +629,7 @@ local function get_next_mob_spawn_pos(pos)
 		y_max = pos.y + y1
 	else
 		-- Inner region, y range spans between inner and outer spheres
-		local y2 = math_sqrt( MOB_SPAWN_ZONE_INNER_SQ - d2 )
+		local y2 = math_sqrt(MOB_SPAWN_ZONE_INNER_SQ - d2)
 		if goal_pos.y > pos.y then
 			-- Upper hemisphere
 			y_min = pos.y + y2
@@ -683,7 +680,6 @@ local function biome_check(biome_list, biome_goal)
 			return true
 		end
 	end
-
 	return false
 end
 
@@ -761,15 +757,15 @@ local function spawn_check(pos, spawn_def)
 	-- do not spawn ground mobs on leaves
 	if spawn_def.type_of_spawning == "ground" and (not node_def.groups.solid or node_def.groups.leaves) then return end
 	-- water mobs only on water
-	if spawn_def.type_of_spawning == "water" and node_def.groups.water then return end
+	if spawn_def.type_of_spawning == "water" and not node_def.groups.water then return end
 	-- lava mobs only on lava
-	if spawn_def.type_of_spawning == "lava" and node_def.groups.lava then return end
+	if spawn_def.type_of_spawning == "lava" and not node_def.groups.lava then return end
 	-- farm animals on grass only
-	if is_farm_animal(spawn_def.name) and node_def.groups.grass_block then return end
+	if is_farm_animal(spawn_def.name) and not node_def.groups.grass_block then return end
 
 	---- More expensive calls:
 	-- check the biome
-	if not biome_check(spawn_def.biomes, get_biome_name(pos)) then return end
+	if spawn_def.biomes ~= list_of_all_biomes and not biome_check(spawn_def.biomes, get_biome_name(pos)) then return end
 	-- check if there is enough room
 	local mob_def = minetest.registered_entities[spawn_def.name]
 	if not has_room(mob_def,pos) then return end
@@ -805,12 +801,12 @@ local function spawn_check(pos, spawn_def)
 		return false
 	end
 	-- passive threshold is apparently the same in all dimensions ...
-	return gotten_light < overworld_passive_threshold
+	return gotten_light > overworld_passive_threshold
 end
 
 function mcl_mobs.spawn(pos,id)
 	local def = minetest.registered_entities[id] or minetest.registered_entities["mobs_mc:"..id] or minetest.registered_entities["extra_mobs:"..id]
-	if not def or (def.can_spawn and not def.can_spawn(pos)) or not def.is_mob then
+	if not pos or not def or (def.can_spawn and not def.can_spawn(pos)) or not def.is_mob then
 		return false
 	end
 	dbg_spawn_counts[def.name] = (dbg_spawn_counts[def.name] or 0) + 1