Crossovers

In Doom related crossovers Doom game elements are featured in another fictional universe not related to Doom's setting, or vice versa.

Most instances of Doom related crossovers have occured in fan-made works. Fan-made Doom movies and games that combine Doom elements with other fictional universes have been made.

Among the most famous examples of Doom crossovers is the Wolfendoom modification for Wolfenstein 3D, Doomguy in Duke Nukem 3D & 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.

Fan-made crossover movies and games
http://www.youtube.com/watch?v=p5b_0DHH-HQ 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.
 * Celebrity Monster Dance - a Halloween special that features an Imp and other monster celebrities dancing in a graveyard.
 * 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.