One reason why Mushroom Hill Zone is my favorite in the series.



Other environments I don't see too often are things like studios (Animaniacs, Dynamite Headdy, Sonic Mania) and music/instruments (Ristar, Sonic Advance 2). They've been used enough to notice, but not enough to be staples (not that I can recall anyway). Candy or food themed levels as well (Castle of Illusion, Sonic Colors).