Twilight on Golarion [Pathfinder Campaign idea]

[The Oni]

Been kicking around the idea of a post-apoc setting where something obscenely awful happens on Golarion - cataclysmic enough to see from space and disrupt/destroy basically every civilization on the planet, but not enough to *completely* end all life. A handful of the most well-established cities are doing their best to weather the hazards while dealing with refugees, while most other settlements are just steps from full-blown Dark Sunnian barbarism (unless it's happened already).

The kicker is that the players will all hail from off-world, and are dispatched by various forces to discover the cause and nature of this anomaly. They may be there to help...or maybe screw things up even worse.

My idea is that the civilizations/races/etc. on Golarion and its surrounding planets will be more or less the same, but extrapolated a couple hundred or a couple thousand years. Tech has advanced somewhat - and then everything went to hell when [earth-shattering event] happened, and I'm planning to incorporate the Mecha D20 rules into the setting for interstellar travel's sake (and because it's freaking cool).

I'd like to give the players lots of race options, but I want them to all be fairly unusual and I want them to have decent reasons to be there, but I'm not an expert on the lore.

Player Races:
Lashunta (from Castrovel) - for a benevolent rescue mission, to document the event for knowledge's sake, or possibly both
Triaxian (from Triaxus) - to make sure Golarion doesn't turn into another Eox, because it's right next to them and freaks them the hell out
Lizardfolk (from Akiton - same stats as Golarion lizardfolk but different culture) - colonization?
Shobhad-neh? (from Akiton) (May require CR-tweaking) - definitely colonization
Android? (technically they hail from Golarion, but the tech that makes them is implied to be otherworldly and could belong to another race) - probably to just document the event
Dragonkin (from Triaxus)? Probably right out for player races but they seem like cool allies.

As for the nature of the cataclysm itself I want to avoid "meteor impact" because Golarion already had one of those in canon.

Any suggestions?

[The Oni]

edited for clarity

[malonkey1]

Well, for the cataclysm, how about an invasion of Aberrations and Elder Gods. The Elder Gods managed to wrest control of much of Golarion from the existing deities, and have made those parts of the world ideal for their warped and twisted children, which would of course make it Hell on Earth for pretty much everybody else. The collective faiths of Golarion were only concentrated in the few cities that remained, which is why they were untouched by the Elder Gods. Constant attacks by the beasts have left the citizens on edge and barely clinging to life and sanity. The Aberrations themselves have no idea they're the bad guys, and are simply trying to oust creatures just as alien to them as they are to us from their literally God-given paradise, while trying not to lose their minds and "go native". Basically, each side can have mind-eroding effect on the other. The outside races are coming in to try and understand what happened, and possibly prevent it from reoccurring elsewhere.

[Alleran]

There's a relatively popular thread on the Paizo forums that you could tap for inspiration here, basically putting together a post-apocalyptic setting where every Adventure Path had the worst or nearly the worst possible outcome, and the PCs failed at every turn. Last I checked, it was:

1) Karzoug is awakened.
2) The Great Old One Mhar (CR 27) awakens, shredding the mountain range nearby and bringing a host of lesser Lovecraftian entities into the world with him.
3) Korvosa is depopulated as Queen Ileosa replicates the actions of Runelord Sorshen in gaining immortality (possibly mythic status), becoming a CR 20+ entity intent on domination.
4) A meteor strikes Kyonin (replicating Earthfall that ushered in the Age of Darkness) thanks to the actions of the drow, wiping it out and causing massive environmental effects to the rest of Golarion.
5) One of the Spawn of Rovagug is bonded with an Efreeti, causing devastation down near Katapesh.
6) An Archdevil gains a staging point on the Material Plane, in Cheliax.
7) The entire Stolen Lands vanish overnight (granted, with some of the other stuff going on, this is minor, and arguably a good thing considering everything else that's going on).
8) Serpentfolk uprising across Golarion from the Darklands, with a nigh-unkillable living god at their head.
9) The Whispering Tyrant (CR 26 super-mythic lich) is freed.
10) Minkai collapses into the rule of the oni over on the other side of the world.
11) The Shackles falls apart. Ifestus (CR 23 Titan) possibly wakes up, devastating it further.
12) First Emperor Xin regains the Sihedron, becomes another powerful wizard overlord, and a clockwork army numbering in the hundreds of thousands (possibly millions) goes on the offensive.
13) Queen Elvanna ascends to the position of Queen of Witches, with Baba Yaga bound, and leads an army of dark fae and monsters from Irrisen into the rest of Golarion, taking her mother's Winter Collectors and putting them to work spreading Irrisen's winter across the rest of the world.
14) The Worldwound expands. Sarkoris is gone for good as the demon hordes flood out in ever-increasing numbers from a wide-open hole in the Material Plane. Numeria and the Silver Mount explodes when the arcanists there set off a nuclear warhead, the rest of the River Kingdoms are overrun, and so on and so forth.

Any or all of these could be employed, or just be something to draw inspiration from. I honestly wouldn't mind playing in such a setting myself. It would be suitably post-apocalyptic, with a war between Elvanna/winter, Deskari/demons, Xin/clockworks, Tar-Baphon/undead, Ydersius/serpentfolk and Mhar/Lovecraft, all taking place in a world choked by the destruction and ash of a second Age of Darkness thanks to the obliteration of Kyonin via meteor, and filled with the touches of Lovecraftian horror.

[avr]

That's a relief. I thought for a moment someone wanted to introduce sparkly vampires to Golarion.

Aberrations, outsiders and undead are the usual suspects for overrunning the world. You could go with one of them easily, or choose something different ... all of the fey from the first world coming over perhaps. Maybe add some dinosaurs like T.rex to justify mechs on the battlefield.

[SonorousDin]

Sounds like a brilliant idea. I'd love to participate if you're doing it online.

You could throw in the added doom of an impending collision with another source world - Abeir-Toril, Krynn, etc. You could also tap into a deific war, in which Gods are slain and fall to the earth as husks - the divine sparks of which all these evil factions are having enormous wars over to harvest for their own malevolent ends.