I’m working on what I think is a ballpark approximation of my old OD&D Wilderlands setting, having lost literally everything that ever had to do with it other than some Russ drawings. This time around, I’m using Gamma World 1e because it’s a good ruleset and it’s perfect for the Wilderlands because at their core, the Wilderlands are completely bugfuck.
My “Gamma Wilderlands” are not post-apocalyptic in the sense that in the vaguely memorable past. there was a nuclear war and now you play a character named Speshul Ed wielding a STOP sign and wearing Gauntlets of Oven Mitt as he explores the wastes of Norf Merkin. They’re post-apocalyptic in the sense that default OD&D is always post-apocalyptic, i.e., there was this huge war but it was a billion years ago and that’s why everything is 99% magic instead of technology but no one remembers how to make a +1 sword. Just like Dying Earth, it’s so far in the future that the history and tech level of past civilizations are meaningless, although you can still find the odd bit of sufficiently advanced technology.
The base game has three potential PC types: Pure Strain Humans (no mutations), Humanoids (mutants), and Mutated Animals. Mutated Animals are a colossal pain in the ass unless they happen to get mutations to allow them to talk and manipulate items, because those are not baked into the character type, so you end up playing a big stupid actual cow with a couple powers. Accordingly, the two real PC types in standard GW 1e are regular people and mutants.
In most cases, GW radiation kills you. In a few cases you live but it gives you some potato-tier defect, and in a very few cases, it gives you cool powers. The people who got the cool powers are the setting’s magic-users, priests, holy warriors, etc.
In the City-State is the world’s only known temple of Vroonops, the Weird God. Vroonops has no worshipers other than the Invincible Overlord, and in fact it’s illegal for anyone else to worship it or otherwise pester it. There’s a ceremonial Temple Guard but they’re even more freaked out than everyone else. No one has any idea what the Weird God looks like and people are fine with that.
In the main sanctuary of its temple are lots of magic mouths that yell, cuss, belch, moan, whistle, make flatulent noises, and otherwise maintain a continuous maddening din. For reasons known only to himself, the Overlord has an entire corps of scribes assigned to the mouths to transcribe their every word and noise. Whenever a mouth gets tired and takes a time out, a lackey rushes up and scrapes its tongue-scum into a sacred receptacle and carries it off to a reservoir before the mouth starts feeling peppery again. This has gone on for a very long time.
Anyone may volunteer to spend a year as a lackey on mouth duty. At the end of that year, the volunteer has the option to descend into the grottoes beneath the temple, saturating themselves in the Weird Energy therein.
The overwhelming majority of supplicants die. Most of the rest end up all fucked up with no positive mutations, just defects, somewhere on the spectrum between the remake of The Hills Have Eyes and I Have No Mouth and I Must Scream. Depending on their degree of fuckiness, these unfortunates either wind up as low-caste menials on the fringes of the City or they just gloop around in the grottoes forever.
The lucky few who come back out with super powers are free to set themselves up as wizards, priests, false gods, knights errant with quills and laser eyes, or whatever. Those are the PC mutants. If they’re feeling particularly passive-aggressive, they can, in a show of mock largesse, take on the fucked up mutants as minions.
NOTE: I’m assuming that cultures other than the CSIO have their own ways of doing things, like embarking on a vision quest into the Weird Energy Wastelands or going into the sacred glowing grove to get Evil Deaded by a tree, etc. Just haven’t really thought about it yet.