I don't know if we're in isolated case, but it looks to me as if the update to 1.8.7 totaly killed mob spawn rates. Our players are complaining and in desperate need for more mobs! Here I stand all alone in the end world, contemplating a big total of 5 endermen on the whole island! Edit: I've raised the monster cap in bukkit.yml from 70 (default) to 100. Now I'm looking at 12 endermen.