*Mr. Mxyzptlk, however you pronounce it, always spells trouble! Not even Superman was invulnerable to this impetuous imp's magical misdeeds! Every 90 days, when Mr. Mxyzptlk left his own demented dimension to wreak havoc on earth, he was honor bound to return home if - and only if - the Man of Steel could trick him into performing some strange stunt of Mr. Mxyzptlk's own concoction! *Source: Back of Card