Kcalb Raven

Chosen one {1}{b} (You may cast this creature for its Chosen One cost if you sacrifice either a black creature or a bird creature while casting it)
Whenever you gain life, you may lose that much life instead. If you do, flip a coin. If it is tails, put a creature from your graveyard onto the battlefield under your control. Exile it at the beggining of your next upkeep. If it is heads, do the same but with target opponent's graveyard.