Shotgun Guy/Doom 64

The Shotgun Guy makes an appearance in Doom 64, but interestingly enough, it uses the sprite of the Former Human, but with a different palette applied to change his suit to more like the original Former Human, making both monsters almost impossible to differentiate in the game's darkness. In this game, Former Humans have green pants, while Shotgun Guys have grey ones. They first appear in MAP01: Staging Area.