The Imperial Warren

{t}: Add {c}.
Whenever a creature you control attacks and isn't blocked, you may exile it face down.
Whenever a creature you control attacks and isn't blocked, you may pay {2}. If you do, return that creature to it's owners hand and put a card exiled
with the Imperial Warren onto the battlefield
tapped and attacking. (It replaces the other creature
as an unblocked attacker).