Doomsday Ghosts are ghosts that originate from within the Doomsday Door.
After doomsday plunged Earth into eternal darkness, the Doomsday Door was set to open and release poltergeist energy. The energy would then replace the physical world with a more supernatural version. The Doomsday Ghosts would also be released and govern the new world. 
They appeared earlier than doomsday in the New York subway. Some are shown to be able to fly. The Ghostbusters didn't directly deal with the ghosts, however the Proton Streams brought the ghosts back into the Power Flow Core.
- In the first draft of the "Knock, Knock" script, J. Michael Straczynski leaves a note suggesting Making Ghostbusters for inspiration on the Doomsday Ghost designs. 
- ↑ Egon Spengler (2009). The Real Ghostbusters - "Knock, Knock" (1987) (DVD ts. 10:30-10:33). Time Life Entertainment. Egon says: "Eternal darkness and the Earth will be governed by ghosts."
- ↑ Straczynski, J. Michael (2009). The Real Ghostbusters Complete Collection Volume One Disc Five, "Knock, Knock" Script p. 9. CPT Holdings, Inc. Line reads: "(NOTE: See Making of Ghostbusters for some additional ideas on subway monsters."