He's in the attic of the toilet room, and when you hit him he starts talking about the backstory of Juice Galaxy (I believe). If he's just some throwaway character then that's okay, but I'd love to see him appear in other places before boss areas to talk more about what happened, like he's some time-traveling deity/hallucination that helps you figure out what happened in the world.
Also, what's up with Mrs. Slithers' students being skeletons and other assorted enemies? Did she prevent them from ever leaving Juice School and somehow they became undead revenants?