Mandalorian Ambusher

Morph {1} (You may pay {1} instead of the
casting cost of this card to lay it face down
as a 1/1 morph creature. You may pay its
casting cost at any time to turn it face up.)
If you turn Mandalorian Ambusher face up
while an opponent is attacking you with
three or more creatures, destroy up to three
target attacking creatures that player controls.