I'm trying to come up with a list of some good universal singleplayer/coop shooter gameplay modifiers - stuff that could work in Doom, Quake, Duke or most other classic shooters. So far I've got:
>ungibbed enemies resurrect after a while
>vampire mode: lose health over time, but drain health from enemies (potentially exceeding normal max health)
>piñata mode: some enemies gain excessive health but move very slowly and drop a lot of random pickups upon death
>random enemies get buffed in different ways (more damage, damage resistance, faster speed, etc.) and then drop a timed version of their buff upon death
>enemy multiplier... pretty obvious
>modifier where all damage (given or taken) is doubled
>weapon and ammo pickup randomizer
>excessive gibs and blood effects, possibly combined with double explosive radius
>random spawning of explosive barrels or other hazards
>spooky mode: map gets covered in excessive fog and/or enemies are invisible until they attack
>mode where gravity is lowered and any damage will knock things around
Am I missing anything?