Vena, Herald of Nishara

+3: Sacrifice a nontoken creature card, deal damage equal to its power to an opponent or a plainswalker an opponent controls.
-4: Lose 3 life, then deal twice that damage to an opponent or a creature an opponent controls.
-15: Vena, Herald of Nishara deals damage equal to the number of cards in graveyards to target an opponent or a creature an opponent controls.