Kalseax, the Stormbreath

Flying, haste
Whenever Kalseax attacks or becomes the target of a spell you don't control, exile the
top card of your library. Until end of turn, you may play that card, and you may spend mana
as though it were mana of any color to do so.
If you don't, target opponent discards a card.
When Kalseax, the Stormbreath dies, you
draw three cards, then discard a card.