Minecraft wiki entry for Zombified_Piglin, associated text: Zombified piglins can spawn in nether wastes, crimson forests, nether portals, and from pigs struck by lightning or from piglins or piglin brutes in the Overworld or in the End. They have a 5% chance of spawning as baby zombified piglins. Zombified piglins do not spawn on top of nether wart blocks. Like other naturally fireproof mobs, they can spawn on magma blocks.