The Madcap Jester is a rare Legendary Creature — Clown Wizard card from Mystery Booster: Commander Edition (MBC), collector number 44.
Whenever The Madcap Jester attacks, each opponent exiles the top card of their library. Whenever a spell or ability you control causes one or more cards to be exiled from an opponent's library, you may play those cards until the end of your next turn. Mana of any type can be spent to cast spells this way.