Minecraft wiki entry for Mob_grinder, associated text: Although a campfire damages mobs slowly, it works reasonably well on any mob without fire resistance. Most hostile mobs (creepers, zombie variants, illagers, spiders, etc.) die in less than 10 seconds in a campfire. A campfire kills an iron golem in about 50 seconds. A campfire killer does not work well on witches, because they give themselves potions of Fire Resistance and Healing. A witch can survive indefinitely in a campfire, so if a witch gets stuck in this trap, it should be killed manually.