E1M1 with 20% population and groups of 1 to 10 monsters, plus item randomization
This "AI Director" is a very simplistic attempt at something akin to Left 4 Dead's AI Director: spawning monsters based on in-game factors to keep things interesting as you play. It creates spawn rosters of all the monsters and (optionally) all the items on a map, removing them in the process, then uses that same roster to spawn new monsters and items at randomized positions. This means a map that normally has a lot of imps will still have a lot of imps, a map that didn't have a chaingun spawn in it still won't have one. However, it also means a map that had one hell knight could have more than one -- and in unexpected places. Or it could have none at all.
The settings menu includes options for adjusting how many monsters spawn in place of old ones, how frequently new monsters spawn in over time (which can also be disabled entirely), and adjusting how many monsters are placed at the start of the map. There are more settings, each hopefully described well enough within the menu itself for you to figure out how it all works together. There is even a setting to make spawns over time less frequent and numerous when players are injured -- and, for that matter, more numerous when players are supercharged!
I find that this can make IWAD maps feel fresh again, and I like that I can adjust it to turn maps into slaughterwads or casual strolls.
One difference between the spawns-over-time with my "AI Director" as opposed to DCS is that this mod tries to avoid teleporting monsters into the map where the player can see them. Instead, it quietly spawns groups of enemies out of sight at a minimum distance, so that you might stumble upon them or be surprised by new foes in a room you'd cleared earlier.
Download v0.2 on GitHub!
Moderator Note: Version 0.2 has a bug in recent versions of GZDoom. Please download and use the "master" version in the meantime until Josh does a new release: master.zip
While the current state of this mod does not take incredibly many factors into account when spawning monsters mid-game (players' health and armor if "Dynamically Soften Spawns" is enabled), I plan to add dynamic moments of higher and lower intensity spawning, and possibly even dynamic item spawning adjustments based on things like player ammo levels. For now, this is essentially a highly customizable randomizer, but I felt it had reached a point where it was well worth sharing.
Spoiler: Setting Recommendations