Well I fixed up my retarded Mancubus so that he actually moves. He can't chase the player yet, just wonder around, but it's a start. Also from looking at the Doom source and some questions on DoomWorld, it appears that Dooms monster AI is incredibly simplistic, so it shouldn't be that hard to implement(famous last words here).
I'm in the process of adding fonts and weapons now.
(Yeah I wish I hadn't zoomed out so far)