Karashima, Shadow Sakura

Master of Ninjutsu {2}{u/b} ({2}{u/b}, Return an unblocked attacker you control to hand: Put this card onto the battlefield from your hand or Command Zone tapped and attacking.)
Whenever Karashima, Shadow Sakura deals combat damage to a player, you may discard your hand, if you do draw that many cards.
(This creature's power and toughness are equal to the number of cards in all graveyards.)