Sash and Waistcoat, Unmen [Mystery Booster: Commander Edition]

Whenever a face-down creature attacks one of your opponents, it can't be blocked this combat.
{3}: Manifest the top card of your library. Any player may activate this ability but only as a sorcery. (To manifest a card, put it onto the battlefield face down as a 2/2 creature. Turn it face up any time for its mana cost if it's a creature card.)