Superman #119

Superman faces one of his most bizarre challenges yet when he must outsmart Mr. Mxyzptlk, the mischievous imp from the fifth dimension who delights in tormenting the Man of Steel with his reality-warping pranks. The only way to send Mxyzptlk back to his own dimension is to trick him into saying or spelling his own name backwards, leading to a battle of wits between Superman's determination and the imp's chaotic magic.