I'm currently making a mod that allows you to change some of the conditions where mobs spawn. For instance, you can disable slimes globally, get rid of those icky ghasts in the nether, stop squids from spawning everywhere, add mushrooms to other biomes, or even rid the end of Endermen.
Also, it will be compatible with Mobs from mods.
It is almost done coding wise, but after that I would like to test and make the GUIs look nicer.
EDIT: Currently implementing a way to save your settings.