In Doom related crossovers Doom game elements are featured in another fictional universe not related to Doom's setting, or vice versa.
Among the most famous examples of Doom crossovers is the Wolfendoom modification for Wolfenstein 3D, Doomguy in Duke Nukem 3D and Quake III Arena, and the secret levels of Doom II, MAP31 and MAP32. The secret Doom II levels are based on Wolfenstein 3D maps and feature the SS Nazi enemy from the same game along with a cameo by the Commander Keen character. In Doom 2 the Way id Did, the secret levels are themed after Commander Keen games; the first for MAP31 and the fourth for MAP32.
Fan-made crossover movies and games
- Celebrity Monster Dance - a Halloween special that features an Imp and other monster celebrities dancing in a graveyard.
- Fan 9 From Outer Space - an early Halloween special made to also be a Friday the 13th special since August was the month for Friday the 13th the year this was released. This is a parody of Plan 9 From Outer Space featuring the Doom Imp as the captain of the ship who embarks on a journey to Planet Nisa.
- Grand Theft Auto: Nick Rebellion - Doom Imps chase after escapees of the warzone in Weinerville.
- Grand Theft Auto: Weinerville - Doom Imps take over Weinerville.
- NEDM Club Remix - a music video in which Doom and other media make cameo appearances.
- Mushroom Kingdom Fusion - a Super Mario-based platformer game with elements from other games including Doom.
- Ultimate Doom Fantasy - Final Fantasy mixed with Doom.
- A Voyage to Planet Nisa - A sequel to Fan 9 From Outer Space where Imp and Dracula get marooned only to find out they have arrived to their intended destination after they see McZee.