Yoreena, Rage Caster

Whenever you cast a spell from your hand,
exile the top cards of your library equal to it
mana cost. You may play a card with lesser
mana value among them without paying its
mana cost. Otherwise, put that card into
your hand and Yoreena deals damage equal to that cards mana value to any target. Put the other cards on the bottom of your library in a
random order.