Yow. That's way too good. Just having a 5/2 vanilla black creature for 4 mana would be about on par with common power levels (See: Dross Crocodile). Adding an ability that allows you to steal a creature upon it's death pushes it into the upper echelon of power. Making it really easy to kill off on top of that makes the card simply ridiculous.
Plus, permanently stealing creatures isn't really black's strong suit and hasn't really been used since Alliances. And that card (Ritual of the Machine) was much less powerful. If I were designing this card to be a fair, balanced rare, I'd probably offer something like this:
Cardname 2BU
Creature - Skeleton (2/3)
Possession 3 (When this creature is put into a graveyard from play, you may put a possession counter on target creature with converted mana cost of 3 or less. As long as the counter remains on that creature, you control it.)
Whenever ~ deals damage to an opponent, sacrifice it.