Knock, Knock

S2, E1: When a group of subway construction workers accidentally uncover an ancient door, that is not meant to be opened until Doomsday, their persistence accidentally triggers the doors opening, which sends incredible amounts of poltergeist energy surging through the New York subway system, transforming the trains into worm-like monsters. The Ghostbusters are called in to deal with it, and Egon discovers that if they don't close the door soon, the entire world will be transformed into a twisted and barren wasteland of ghostly and demonic creatures that will replace all of humankind and civilization the world over.