“The Reign of Emperor Joker, Part 5 of 5: He Who Laughs Last!”
Though Joker's control of the universe is absolute, Superman points out that Joker cannot will Batman out of existence because he cannot get Batman out of his mind. With the realization that he will never be rid of Batman, Joker breaks and returns his power to Mr. Mxyzptlk, who restores the universe. But Batman's mind has snapped from all the torture he witnessed at the hands of the Joker, and the only way to restore him is for the Spectre to transfer the pain and trauma to the Man of Steel, who heroically shoulders the burden.