After the lighting change in 1.18, slimes in swamp biomes are the only mob to still spawn at light level 7 compared to light level 0 for all other Overworld hostile mobs.
How to Reproduce:
Create a superflat world with the following preset:
"minecraft:bedrock,127*minecraft:dirt,minecraft:mycelium,minecraft:brown_mushroom;minecraft:swamp;"
Make sure 'Generate Structures' is set to OFF.
The ground is high enough to be out of the range of slime chunks, but within the range of where slimes can spawn in swamps.
Mycelium ensures the brown mushrooms don't break.
Brown mushrooms emit a light level of 1 which, due to them blanketing the entire world, should prevent the spawning of all hostile mobs.
Enter the world.
Enter the command "/time set midnight".
You should see nothing but slimes spawn, proving they have different spawning requirements in Swamps from other hostile mobs.
Comments 4
Is there a possibility that Ulraf was thinking of only of slime chunk spawning when writing that tweet and swamp slime spawns are therefore an oversight?
To clarify: The light level changes only apply to block light (i.e., light emitted by blocks), not sky light (emitted by the sky, i.e. sun and moon). Those are two distinct values.
At night, there is a sky light level of 7. If the spawning requirements would include sky light, no mobs would spawn during night time at the surface, which is not desirable.
That's what Ulraf was talking about in his tweet.
Now, if they can still spawn in a block light level of >0 that might still be a bug.
This is intended. See tweet by @unknown