If you enter "RAMBO" as a cheat code, then you get all of the weapons.
If you enter "COCKADOODLEDOO" as a cheat code, you get turned into a chicken.
If you enter Doom's invulnerability cheat code, "IDDQD", you die instantly. Similarly, entering Doom's all-weapons code, "IDKFA", will strip you of all weapons.
Built on the Doom engine. First game to license a third party engine and starting the trend.