Mr. Mxyzptlk, the imp for the 5th Dimension who often battles Superman, will be appearing on two episodes of Supergirl. Comicbook.com got this confirmed by the CW. Created by Jerry Siegel and Ira Yarborough in 1944, the character has been both a silly, fun villain and at times much more dark and sinister. This won't be the character first foray into live-action, as he appeared on a 1989 episode of the Adventures of Superboy played by Michael J. Pollard, a 1996 episode of Lois & Clark: The New Adventures of Superman played by Howie Mandel and a 2004 episode of Smallville as played by Trent Ford.Only the Superboy series tried to give the character the classic look.
How the character will appear or who will be playing him on Supergirl has not been revealed. There is some speculation that he may be involved in the Supergirl / Flash musical crossover coming up. It would not be out of character for Mr. Mxyzptlk to force people to sing for his amusement.
If they do any legacy casting here, I'd really like to see Howie Mandel again.
I suddenly very much want him to meet John Diggle.