Mr. Mxyzptlk is back, but doesn’t want to be, in the Pasko, Swan and Chiaramonte tale in Superman 335 (May 1979).
Mxyzptlk, who is due to get married,finds himself exiled to Earth after turning the mayors children into chickens. Saying his name backwards will no longer send him back to Zrfff.
Superman gets bitten by a extraterrestrial creature in his zoo, and the animal’s venom is slowly turning Superman into a lizard type creature, as well as removing his powers. He wants Mxyzptlk to use his magic to cure this, and promises to figure out a way to send him back home after, but the imp does not trust Superman, and refuses to cure him unless Superman sends him home first. It’s a stalemate, so Mxyzptlk keeps using his magic in hopes of infuriating Superman enough to send him back.
Instead, Superman cons Mxyzptlk, telling him that he can see his fiancee in deadly danger back in Zrfff. Mxyzptlk removes the effect of the venom, and finds himself transported back anyway, for doing a good deed.
The final laugh is on the imp, when he discovers that his bride has been using her magic to alter her appearance. Perhaps this resulted in a divorce, as we never see or hear about her again.