Action 460 (June 1976) was the third issue of the series that I bought. It is the beginning of a four-part story, which made me buy the next three issues, and got me buying the series regularly.
The story, by Bates, Swan and Blaisdel, begins in a very low-key manner, with Clark Kent riding the bus to work. Steve Lombard winds up in the same coach, his sports car in the shop. But neither man is prepared when a glowing alien being suddenly shows up in the back of the bus.
This creature is clearly none too find of Superman, and appears almost equally matched in strength. He vanishes in the middle of the fight, and Superman is pretty sure that he turned back into whatever human guise he had been using on the bus, before he transformed.
Superman is dead on about that. This is Karb-Brak, from a planet in the Andromeda galaxy. He is fatally allergic to all of his people, and was sent to live on Earth, just in order to survive. His human guise is a construction worker, Andrew Meda. Superman evokes the same allergic reaction that Andromedans did, so Brak decides he must kill Superman to save himself.
He tracks the energy, and sees Clark Kent and Steve Lombard working out together in the WGBS gym. He starts to transform, but does not notice Clark take off and become Superman. Assuming Lombad must be Superman, he breaks in to kill him.
Though this is billed as a Mr. Mxyzptlk story, the real star of it is the recently introduced Jon Ross, whom Mxyzptlk chooses to pester.
Jon has heard about the imp. After Mxyzptlk turns Pete Ross into a statue, Jon decides to play along with him, pretending to enjoy it all, and bide his time.
Mr. Mxyzptlk genuinely enjoys having a partner in his lunacy, and is unprepared when Jon traps him in a creation of his own making, which he cannot escape from, short of returning to his home dimension.
So this is kind of like a “private life of Jon Ross.”