I'm trying to farm Wither Skeletons and Ghasts, and they just do not seem to spawn. I've gone back and forth through four different Fortresses only to see a total of about five Ghasts and six Wither Skeletons. On top of that, I don't see too many Zombie Pigmen, maybe two or three Magma Cubes, and not a single Enderman or normal Skeleton.
I don't think the system has changed, but works different then what we used to have via 4J's version, and the PC version.
What I have figured out so far, is that it looks like mobs spawn out to about 5 chunks from the player in all I directions. But mobs don't seem to 'despawn' ever if you move so that the mob is outside of the 5 chunk boundary around you.
What I have tested is to have mobs spawn and then moved away from that area, so that the spawned mobs were more then 5 chunks away from me, in fact I went over 128 blocks from said spawned mobs. Waited till mid day, and moved back to the area, only to find said mobs spawn back in, and begin burning in the sunlight. These mobs should have long since despawned. I even did the same test only instead of returning to the area at mid day I first set the game to peaceful, waited a minute, then set it back to hard, and returned to the area, again same mobs were found and begin burning.
This leads me to believe that mobs are cached, and said mob cache is NOT cleared when the game is set to peaceful, nor do mobs despawn so long as they are outside of the 5 chunks around the player. We do know that up to16 chunks are loaded around the player, but NOT ticked, however are mobs in this area counted towards are cap? Since they are not ticked they likely can't despawn, I believe there is a serious bug in the spawn code.
What I have found that works is to set the game to peaceful, walk all around where you normally patrol, this will despawn mobs as they are loaded in, once the area has been completely walked through set the game back to your default difficulty, wait a bit and do a patrol, you should see loads of new spawns.
The wither skeletons and normal skeletons have not respawned in the three nether fortresses in my world. Ghasts and pigmen abound, but the skeletons don't seem to spawn after slaying them. There is a bug report on it, but I'm too lazy to go look up the link....
I saw it. I honestly think there's some kind of bug with mob spawning in general. I saw one Slime over the course of three nights, and a total of three wolves across several forests and taigas. This ridiculously low spawn rate is making it impossible to do many of the mob-related achievements.