Wow

Wow (or wow.wad as a file) is a 1999 PWAD by Paul Thrussell replacing E1M1 of Doom. It is often mentioned in "worst WAD" discussions and forum threads, and was featured in Doomworld's Top 10 Infamous WADs. The author later admitted he had created it "when [he] was about ten years old" and uploaded it because he "had a great fascination with putting anything [he]'d created onto the internet"[1].

Description
The map is comprised of a single room with a BFG9000 and 3 energy cell packs for it. There is no exit, and the main feature of the level is the "illusio-pit": a pit with a fake floor effect hiding it situated under a quivering torso hanging from the ceiling, with a cyberdemon in it. The pit is thus invisible until the player falls into it, at which point much of the screen is filled with hall of mirrors effect because of the missing textures. The text file accompanying the WAD gives the following explanation for the pit:
 * A cyberdemon has escaped from a lab, where they are trying to find his weakness. He was injured by a marine, which was made short work of, and he was trapped inside a illusio-pit.

Similar "illusio-pits" have been used in parts of Joke WADs such as Mock 2: The Speed of Stupid and The New Adventure as tributes to Wow.

Additional information:

The so called "Illusio-pit"'s radius is about 2 cyberdemons.

The height of the "illusio-pit" is about a cyberdemon and a spider mastermind.