here's a minor bug-let that I just noticed while messing around with the latest release of the eternity engine, although it could very well exist in all other doom engines, for all I know.
Doom 2, Map 32, Nightmare. The Commander Keens, even if left alone, will eventualy attempt to respawn. That is, even they havn't been so much as scrathed, they will emet the green respawn fog and play the teleport sound effect.
While I'm on the subject of that, I'd also like to mention a little one I had been making use of when I first saw that one, which I've known of for a while
In the console, using the Spawn command in conjunction with any paramater it doesn't recognise will cause a sort-of player-clone to be spawned. It just stands there. Monsters don't pay any attention to it, yet attacking it causes you to take damage. through use of these clones, I've had a fairly easy time taking up the art of self-zombifacation. Although I still havn't determined the *best* situation for it, I seem to have the most luck with piling them up in a corner, cheating a chaingun into my hands, and opening fire upon them.
Oh, and some things about being a zombie: Avoid health, as it makes you alive (monsters will see/attack you again), but weaponless. Becoming a deity has the same result, and neither cheating for, nor picking up weaponry will help.
I hope I havn't wasted too much of your time.