Back to back appearances by Mr. Mxyzptlk AND Krypto? Okay, let's see. In Superman #154, the Imp from the 5th Dimension annoys Superman by making all animals talk. Not just garden variety pets and mounts, but Krypto and Streaky too. Lest the easily excitable citizens of Metropolis FREAK OUT, Superman has his super-pets calm things down with an ingenious scheme.
In Superman #155, Mxyzptlk is back in a crazy story that has Superman lose his powers, a professional wrestler gaining them, strongman heroes from myth being summoned, and a crook using the situation to get his loot from a cave bouldered over since he hid it there. But wait, it was all a scheme to get the crook to reveal his hiding place! Superman was the wrestler, the wrestler was Superman, the mythological strongmen were members of the Legion of Super-Heroes, and Mxyzptlk?