Masters Edition

Ydwen Efreet

Whenever you're attacked, flip a coin. If you lose the flip, Ydwen Efreet can't block this turn.

Whenever Ydwen Efreet blocks, flip a coin. If you lose the flip, remove Ydwen Efreet from combat and it can't block this turn. Creatures it was blocking that had become blocked by only Ydwen Efreet this combat become unblocked.

Arabian Nights

If you choose to block with Ydwen Efreet, flip a coin immediately after defense is announced; opponent calls heads or tails while coin is in the air. If the flip ends up in opponent's favor, Ydwen Efreet cannot block this turn.