https://deadline.com/2019/12/supergirl-thomas-lennon-recur-season-5-cw-series-mxyzptlk-1202805769/

He'll recur as Mxyzptlk (https://en.wikipedia.org/wiki/Mister_Mxyzptlk), aka “Mxy,” an impish, reality-bending trickster from the 5th Dimension.

Thomas Lennon says goodbye to Supergirl, recounts how Melissa Benoist helped him learn to pronounce "Mr. Mxyzptlk" (https://www.thewrap.com/thomas-lennon-supergirl-mr-mxyzptlk-melissa-benoist-amazing-at-everything/)

“I wasn’t great at saying the name out loud," Lennon says of his character. "And then, Melissa, who’s amazing at everything, just stepped in and she was like ‘Mr. Mxyzptlk!' And I’m like, ‘Oh, that’s how you say it!’ I forgot. I knew that that’s vaguely how you say it, but she said it with such confidence that every time I say the name, I’m just trying to remember the way that Melissa says it.”