Vax'ildan, Raven Champion

Menace, haste
Whenever Vax'ildan deals combat damage to a
player, exile the top card of that player's library
face down. You may look at it and spend mana
as though it were mana of any color to cast those
spells for as long as it remains exiled.
{b}: Vax'ildan gains flying until the end of turn.