Loophole Mage

Megamorph {1}{u}{u} (You may cast this card face down as a 2/2 creature for {3}. Turn it face up any time for its megamorph cost and put a +1/+1 counter on it.)
When Loophole Mage is turned face up during the declare attackers step, you may reselect which player or planeswalker target attacking creature is attacking. When that creature deals combat damage to a player this turn, turn Loophole Mage face down.