Master Splinter, Sensei

Commander ninjutsu {u}{b} ({u}{b}, Return an unblocked attacker you control to hand:
Put this card onto the battlefield from your hand or the command zone tapped and attacking.)

Whenever a Ninja you control deals combat damage
to a player, reveal the top card of your library and
put that card into your hand. Each opponent loses life equal to that card’s mana value.