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

Whenever Sub-Zero deals combat damage to a player, you may tap target creature that player controls and put a stun counter on it. If you don't, you may destroy target creature that player controls with a stun counter on it.

Whenever Sub-Zero deals damage to a creature, tap that creature and put a stun counter on it.