6. 3 0PM, FOX8 Because Supergirl isn’t silly enough, tonight’s episode digs up retro Superman villain/troublemaking nerd Mr Mxyzptlk. When he of the unpronounceable name (guest star Peter Gadiot) drops by National City to tell Kara (Melissa Benoist) he’s got a crush on her, she tries to let him down gently. Cue city-wide destruction. estruction.