Kabuto Yakushi

Ninjutsu {3}{b} ({3}{b}, Return an unblocked attacker you control to hand: Put this card onto the battlefield from your hand tapped and attacking.)

Whenever Kabuto Yakushi deals combat damage to a player, exile the top card of each players library. Until end of turn, you may play one of those cards. If you cast a spell this way, pay life equal to its mana value rather than paying its mana cost.