Corrupted Spiritcaller

Manashift {1}{b}{b} (You may cast this spell for its Manashift cost. If you do, it becomes black and loses all other colors.)
When Corrupted Spiritcaller enters the battlefield, exile target creature card from a graveyard. If Corrupted Spiritcaller is green, gain life equal to that card's toughness. Otherwise, target player loses life equal to that creature's power.