Hidden Pit

{t}: Add {1} to your mana pool.
Hidden Pit comes into play face down and can be
turned up at any time for its Activate cost.
Activate {4}
When Hidden Pit is turned face up, for each
attacking creature without flying flip a coin,
for each flip you win that creature's controller
sacrifices it.
{5}: Return Hidden Pit to its owners hand.
"AAAHHHRRRGGG—!" —Malcom, last words