Examples I got away with in The Watch House included Natalie discovering she was a fairytale princess, Victorian times leaking out of a cursed mirror and infecting the world around it, a descent into the underworld complete with an army of evil ghosts including undead Nazis, a Days Of Future Past post-apocalypse nightmare, and (borrowed with thanks from Eerie Indiana and latterly used in Supernatural) the one where William and Sunita discovered The Watch House was actually a TV show and everybody else was a bunch of actors.
So as long as your players are up for it, you can get away with just about anything. The only real trick here is going back to normal the week after. Too much of this and you could end up in total format meltdown - The Xena Syndrome. So only go this kablooey once a season. Maybe twice.
Example: The Facts In The Case Of Billie Griffin
The players take on the role of a group of paranormal investigators, searching the supposedly haunted Mason House at the edge of town, piecing together clues relating to the disappearance of the band Will Play For Food five years earlier...
Example That Apparently Supernatural Did: Video Killed The Vampire Slayer
A paranormal reality show (OB crew, night vision cameras and all, more Most Haunted than Mysteries Of The Bizarre) comes to town, looking into stories of strange occurrences around campus. The completely sceptical production team miss blatant clues, look the wrong way as vampires run past, accidentally alert monsters the band are hunting and allow them to escape, enlist false witnesses to produce an inconclusive and untrue story, and generally cause trouble that means the band have to save the world from the forces they've inadvertently allowed to threaten it. And all while Hope practices her telegenic screaming and fainting as she tries to get an interview which in the final edit lasts three seconds.