Action Comics #583 Facsimile Ed

Lois continues to relate how when Superman was holed up in the Fortress with his closest friends, being attacked by Brainiac (having taken over Luthor's body), the Kryptonite Man, and the Legion of Super-Villains, he realized who the mastermind behind it all was, and called on Mr. Mxyzptlk to show himself; Just as Superman sent Mxyzptlk into the Phantom Zone, Mxy fled to his own dimension, tearing himself apart; Having taken a life, Superman exposed himself to gold kryptonite and retired.