So I might be interested in this...

Ah hell I AM interested in this. Though how would you feel about a character who can call on demons?

The basic idea is this. Character can call on a demon to which he was bound from birth, to accomplish a specific affect in the world. In this case, withering a person they make skin to skin contact for the period of a minute. Of course they can't just "use" this power whenever they want. In order to get it, they must first shed their own blood before calling upon the demon to which they are bound. If they do not shed the expected amount, in this case a medium gash across the palm or some other part of the body, then the demon will refuse their call. Also, if they are gagged, and thus cannot call upon said demon, they are powerless even if they cut themselves.

Furthermore, there'd be different negative domains demons lord over, so you wouldn't be able to use it to bend reality or enhance yourself, or have a medley of different powers at once.

EDIT: This idea might introduce a 'Heaven' or 'Hell' of sorts, but I'd probably treat those as separate dimensions with beings who operate on different principles rather than how they are traditionally portrayed.

EDIT 2: I see a sort of overarching Astral Realm thing from Harbinger of Ferocity, so assuming this idea goes anywhere and it's alright, I'd just make Hell and Heaven some old planes that exist within that.