Imps, amirite? Can't live with'em. The vindictive Princess Nyxly is making trouble in Metropolis, and Supergirl ended last week's episode by calling an audible. The once-adversarial Mr. Mxyzptlk proved himself a (still somewhat chaotic) ally of the Superfriends last year when he appeared in one of Season 5's best episodes, "It's a Super Life," and…