Affects Version/s: Minecraft 1.8.8, Minecraft 1.10.2, Minecraft 16w42a, Minecraft 1.11, Minecraft 1.11.2, Minecraft 17w06a, Minecraft 1.12.2, Minecraft 18w03b, Minecraft 18w20c, Minecraft 18w22b, Minecraft 1.13-pre5, Minecraft 1.13.2, Minecraft 19w08b, Minecraft 19w09a, Minecraft 1.14.2, Minecraft 1.14.3 Pre-Release 3, Minecraft 1.14.3, 1.14.4, 19w34a, 19w38b, 1.15 Pre-release 6, 1.15.2, 20w17a, 20w21a, 1.16 Release Candidate 1, 1.16, 1.16.1, 20w29a, 1.16.2 Pre-release 1
Fix Version/s: None
Slimes are spawning specific to the moon phase and the swampland biome, but not in the swampland hills.
- Create world type: Superflat, Customize, Presets:
Change number of dirt blocks to 62 and change biome from plains to swamp_hills
- /time set night (you'll see the full moon, otherwise add 24000 until you could see it)
- /gamerule doDaylightCycle false
- Kill all other mobs with command blocks
You can repeat this and use the swamp biome and you will see many slimes in seconds.