Harbinger, Outworld Destroyer

Flying
Whenever Harbinger, Outworld Destroyer deals
combat damage to a player, if you have more
cards in hand than them, that player mills that
many cards. If not, draw 3 cards, then discard a
card.
Harbinger, Outworld Destroyer gains +X/+X,
where X is the amount of mana in your mana
pool.