The bug
Hostile mobs may or may not spawn on slime blocks. It is randomly limited to selected areas. This does not seem like an intended feature.
Linked issues
is duplicated by 1
relates to 2
Attachments
Comments 40
Hi Kumasasa!
I too, have tried this. However, Slimes would not spawn in the day. I replaced the Slime Blocks with Stone to see if it made any difference, and still, no Slimes were spawned (attached picture).
*Edited because I spelled Kumasasa's name incorrectly. Note that Slimes would not spawn in the same world that I tested previously (the one with the water at night).
"Maybe the hostile mob spawning area is identical with the slime spawning area (slime chunks)"
I believe this is correct, although I have not conclusively tested.
Mark, slimes spawn in slime chunks between Y 0 and 39, however hostile mobs will spawn from Y 0 to 255.
Slime blocks placed in a slime chunk at Y63 (sea level) will not spawn slimes but will spawn hostile mobs. However, if place between 0 and 39 we should find both slimes and hostile mobs spawn.
If slime blocks are placed outside of slime chunks it is my understanding that no hostile mobs will spawn.
As I have said, this is not conclusively tested, but I believe it may be 'as intended'.
As Alec suggested, Slimes will not spawn within a Slime Chunk if it is above Y 39 (excluding Swamp Biomes), although this screenshot proves that it is indeed within the Slime spawning range.
Probably duplicate (or related) to MC-64492.
Can somewhat confirm.
Created a flatworld with the topmost layer made of slime blocks. At night hostile mobs spawn only in certain areas.
Maybe the hostile mob spawning area is identical with the slime spawning area (slime chunks)