“A zombie pigman is a mob that spawns naturally in the Nether and appears in the Overworld when lightning strikes within 3-4 blocks of a pig, which is on very rare occasions, and they can spawn near nether portals, though not very often.”
Common mob in the Nether and it can also spawn in the Overworld when lightning strikes (near) a pig.
Zombie Pigmen often spawn in groups of 4. They are neutral until provoked. When you hit one of them, all Zombie Pigmen in the area will start to attack you. They are immune to fire and lava. Keep in mind that Zombie Pigmen can also use a Nether Portal and therefore go to the Overworld.
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