Yuki, Silent Avalanche

Ninjutsu {s}{u}{u} ({s}{u}{u}, Return an unblocked attacker you control to hand: Put this card onto the battlefield from your hand tapped and attacking. {s} can be payed for with one mana of any type
produced by a snow permanent.)
Whenever Yuki, Silent Avalanche enters the battlefield or attacks, target snow creature can't
be blocked this turn. If that creature is blocked,
it becomes unblocked.