Doppleganger

Deathtouch
3 Reaction {b}{b} (Use this ability only if there is a creature attacking you. If so, then you may pay the reaction cost. Once you do, then deal X damage to that creature, where X is the Reaction number.)
When this creature comes into play, copy target creature. It has all abilities. All activated abilities are payed with {b} instead. It's power and toughness is equal to the opponents creature's power. Gaining life through Doppleganger deals that much damage to every opponent.