Kayn, the Shadow Reaper

Ninjutsu {1}{u}{b}, First Strike
Whenever Kayn, the Shadow Reaper deals
combat damage to a player, exile the top card of
that player's library. For as long as it remains
exiled, you may play it by paying life equal to
that card's mana value.
{u}{b}: Return, Kayn, the Shadow Reaper to its
owner's hand.
"The blood of the fallen will anoint me the
new master."