The last episode filmed.
One of eleven episodes where the Midnight Society didn't leave and douse the fire with the water-bucket (Megan was listening to Andy play the violin).
Inspired by Gaston Leroux's novel The Phantom of the Opera. Possibly inspired by Victor Hugo's novel "The Hunchback of Notre Dame" as well (Michael calls the mutant Quasimodo, meaning he at least reminds him of it).
The close up shot of the clock is also used in "The Tale of the Reanimator" (2000).
For some unknown reason this episode isn't on paramount streaming.