A lot of things in Little Nemo in Slumberland unnerved me as a kid. I think part of it was how quickly the movie went from fun happy dream stuff to literal nightmares.

The Nightmare King from Little Nemo, somehow he combined in my head with the Air Conditioner from Brave Little Toaster, and I had a nightmare that there was an evil living furnace in the back of the house that would suck in anything that went in the room.

The nightmare really had nothing to do with the scene in the movie but I had it after watching