Pillagers are the only mobs (apart from phantoms, see MC-127599) that continue to spawn in the void biome. When I create a superflat world using the void biome no other mob except pillagers (and phantoms) continue to spawn naturally.
Steps to Reproduce:
Create a superflat world with the following preset:
minecraft:bedrock,2*minecraft:dirt,minecraft:grass_block;minecraft:the_void
Change the world difficulty to
Hard
(optional) place a repeating command block (set to either always active, or active with redstone) with the following command:
tp @e[type=!player] @p
Tick sprint the game by a large number of days
Wait for a patrol to spawn (can leave the game running in the background. You will know when a patrol as spawned because they will make noise once teleported to you)
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Can confirm in 1.21:
[media]
This issue takes a bit of patience to reproduce. I have created clear steps to get a reliable result, although it does require waiting.
Steps to Reproduce:
Create a superflat world with the following preset:
minecraft:bedrock,2*minecraft:dirt,minecraft:grass_block;minecraft:the_void
Change the world difficulty to
Hard
(optional) place a repeating command block (set to either always active, or active with redstone) with the following command:
tp @e[type=!player] @p
Tick sprint the game by a large number of days
Wait for a patrol to spawn (can leave the game running in the background. You will know when a patrol as spawned because they will make noise once teleported to you)
Phantoms spawning in void biomes is a duplicate of MC-127599.