However, fortunately it turns out that I am a genius. I realized I don't have to do that at all! The whole point of this game is it's a Roguelike. Randomly generated mazes, no two games the same, right? Why not randomly generate enemy types, too? Let's say that we could come up with an enemy's "challenge rating" by summing up various characteristics: how smart its AI is, what primary and secondary weapons it has, how many hit points it has, how maneuverable it is, et cetera. And let's say that we can also sort them into broad categories: here are guys who attach to walls, here are guys who roam through corridors. Then it should be possible to jumble features together and create enemies of appropriate difficulty to populate each set of levels.
The more I think about this idea the more I like it. (It has additional programmer appeal since I'd be getting the computer to do my work for me, and presumably showing off how clever I am in the process.) Of course there may be a number of feature combinations which are counterproductive or even stupid, but I can burn that bridge when I come to it. Just at this moment, I'm kinda thinking that the hardest aspect of this idea would be creating a distinct yet attractive visual look for each generated enemy type: somehow, the various features an enemy can have are going to need to be clearly visually expressed in their ultimate design.
I'm not sure that any other game has really done this on the scale I'm thinking of, although something tickling at the back of my mind is suggesting at least one indie-type title has tried it before. I don't have anything more than a tickle on that, though. Warning Forever kind of gives off that impression, but I'm pretty sure all the various bosses in that game were hand-designed.