Okay, I just discovered 2 bugs with the final boss.
The first one, is in the cutscene before it, when you grab the Duo Fist and you're supposed to go towards the hole in the ceiling.
If you back up, slowly into the corner of the hole, the small 'mini-cutscene' will activate, but you will get stuck on the ceiling.
Here's an image:
(https://dl.dropbox.com/u/5237238/MM8BDM/Screenshot_Doom_20130313_092656.png)
The second one, is during the actual boss. If you don't move from your spawn point, and spectate, wait for the Evil Robot to charge at you, then move inside of him and rejoin the game. The Evil Robot will then die as you come back.
Also, the explosion cause by the Evil Robot will kill you too.
Also, in a related note, spectating can clone Gamma too.