Imps

Imps are the only passive mob in the Nether. When killed they split into two more, then two again. When those are killed, they drop Imp skin.

Backstory[]

The Nether in the past has been known to launch into states of random chaos. Imps were the solution to this. They were "employed" to assure that evil souls are attracted and contained in the Nether. Nobody knows who or what they were "employed" by. Nobody. Not even the Imps themselves, can even recall. The Imps just mindlessly work, somehow generating a spiritual, gravitational pull to make sure everything acts as it is supposed to. Unfortunately the Imps were obviously designed for one thing only, keeping order. Thus, they have no kind of self defence, save for an odd splitting action that was presumably implemented to attempt to restore order by increasing the Imps in numbers, although this seems to be a failure as a defense mechanism.