Old Demon King

Dethrone (Whenever this creature attacks the player
with the most life or tied for most life, put a +1/+1 counter on it.)
Whenever another source you control would deal
damage to a permanent or player, you may exile a nonland card from your graveyard. If you do, it
deals that much damage plus X instead, where X
is equal to that cards mana cost. This ability only
triggers once each turn.