I've never actually played the game before, but after looking it up I agree the Cacodemon does look pretty similar. I remember years ago I was really into drawing fantasy swords and various weaponry. I went to a youth group back then and some of the guys thought some of stuff was from the game series Halo (most notably my double sword which had two swords that faced the same direction and were connected by a handle, and my gun that had a hand guard that fully surrounded the hand. It also had thin spikes which protruded from the top of the gun (I can't remember their exact purpose -- whether they would fire from the gun or added to the hand guard's defense). I'd never heard of Halo up to that time, or seen any of its gameplay. One of the fellows brought in the game one time during a New Year's Eve party, and I got to play it for the first time. And they were right. Halo's plasma saber and needle gun looked strikingly similar to my stuff.