Battleline Executor

Sleeper {1}{w} (You may cast this card for {3}. Put
this card face-down in an opponent's field as 2/2
creature but it's name is Sleeper Agent. Your opponents
may not look at Sleeper Agent face down cards. You
may flip this card face-up anytime by paying its
Sleeper cost, if you do, resolve all Double Agent effects
and return it to your control.)
Double Agent - Sacrifice an attacking or defending creature you control.