Gunnar, Backstabber

+1: You gain life equal to how much life your opponents lost this turn then discard a card. This ability can be activated on any players turn.
-5: Destroy target creature or planeswalker an opponent controls you gain life equal to its toughness or amount of loyalty counters
-15: Target loses life equal to your total life total unless they sacrifice all creatures they control, sacrifice three lands and discard their hand.