Ambush Mechanic

Ambush {b} (Whenever one or more creatures attacks you, if this card is in your hand, you may play it at instant speed for its Ambush cost. If you do, return it from the battlefield to your hand at the end of combat.)
Costs approximately {0} to add to a 1/1 body. Costs much more with deathtouch: a bit less than {1}. This is worse than flash unless the creature has and etb effect (or similar advantage).