Tonight's new episode of "Supergirl" is titled "Mr. & Mrs. Mxyzptlk", and will air on The CW at 8.00pm ET/PT. DC COMICS' MR. MXYZPTLK HITS NATIONAL CITY When Mr. Mxyzptlk (guest star Peter Gadiot), a magical imp, shows up on Earth and declares his love for Kara (Melissa Benoist), she tries to let him down