Bourne, Dreamer's Apprentice

{2}{u}{g}: Bourne, Dreamer's Apprentice gains flying and hexproof until end of turn.
Whenever Bourne deals combat damage to a player, you may pay {2}{u}. If you do, reveal the top card of your library. You may play that card this turn without paying its mana cost if its converted mana cost is {4} or less. If not, exile it.