“That’s a good question, and it’s not necessarily front and center, but there is very much reference within the other characters,” Peter said. “They’re aware of him and his abilities and his history, because certain people in the episode are kind of surprised by Mxy and then other people say, ‘No, this is his history, and this is what’s going on.’ And so, yeah, there is an awareness of him, but obviously the focus is very much on his relationship with Supergirl.”
It seems likely Mxy at least knows of Superman, judging by the preview for Monday’s episode, which sees Peter’s character in a very Kal-El-esque suit. But it’s not Tyler Hoechlin’s blue and red supersuit from the Season 2 premiere.
“It was a new one. I did actually try on that suit for the initial fittings to get a shape of it, and it fit pretty good, but they like to do things obviously very specific and proper and so I was fitted and I got my own special one with the Mxy M on it. The first Mxy supersuit, I think,” Peter said.
Peter said a “slight backstory” about why Mxy has “genuine feelings” for Kara is revealed in a couple of scenes in Monday night’s episode.