This mod adds craftable mob spawn eggs, crafted by combining a bucket of water, 4 bonemeal, and 4 soulsand. It also adds a new plant named the Soul Plant that drops soul fragments that you can craft soulsand out of. The Soul Plant has some hidden features and can only be harvested during the nighttime.
(by the way, by non-hostile I mean animals and other mobs that run from you when you attack, hostile is everything else..)
Probably a good idea to use the eggs in creative first, to get a feel for it.. Hold right click to throw the egg at the mob.