There are three divine factions: Creation / Weaver / Lilith / Lolth / Spider God / Elves, Transformation / Cthulhu / Squid God / Mind Flayers, and Destructio / nameless devourer that started off by eating its own name /Frog God / Slaad. The Mind Flayers came to the world, bringing their hairless monkey peons and uplifting the local reptilian creatures into servitor races, hence lizardmen, yuan-ti, frog dudes. The Elves came here after them to get some macguffin back off them and wiped most the Mind Flayers out, but the flayers corrupted them in the process, turning Lilith the creator/weaver into the Lolth we know and love. The Mind Flayers are pretty much out of the picture, but their touch is everywhere.
Initial PC races are humans, lizardmen, medusa, maaaaaybe yuan-ti, and some cute little frog dudes, and possibly high elves brought very very low – corrupted and either bloody eyed, sharptoothed albino cannibals (elrics, really), and drow; post some sort of eldritch war tween the elves and the yuan-ti, where the yuan-ti won and now the humans have to deal with them and try really hard not piss them off.
It's low-magic (cthulhu style incantations, no spells, sanity checks for learning magic from forbidden tomes) proto-industrial (pistols and muskets and zeppelins) and divine magic is very rare - the province of secret cults devoted to the spider, the squid, and the toad. initially I want it to be the province of NPCs only, though if any of the players sign up for a bit of arachnotoadsquid worship they get access to divine magic. With suckers and tongues.Mutations abound. Healing accelerants come from alchemical derivations milked from the fleshfarms of jungletoads, and there is always a risk of strange side-effects (there's another random table right there!)
The campaign will start in the Yuan-Ti occupied city of Corbrea, surrounded by vast tracts of nameless jungle. The premise for the berlinesque city was that pre-war it was a human city states' drug haven colony in the midst of the jungle (we're here to lick your frogs!); occupied by yuan-ti during war, still controlled by them post war, but chosen as suitable meeting point tween the yuan-ti empire and the human nations. The yuan-ti remain hidden most of the time, having bred the medusa as human-relations strain to interact better with the hairless monkeys, but there are gigantic orphanages where orphans from the eldritch war are trained by Yuan-Ti their entire lives to play a single part in their "living history", Chinese opera style. Huge parks are dedicated to these continual re-enactments / celebrations of Yuan-Ti domination. Theirs is a bio-genetic surveillance culture. Watching eyes are posted nearly everywhere, with connective nerve tissue leading back to pulsating throne rooms where overseers observe all.
The surrounding jungle is crawling with freakish creatures. Mutant Babbeloons, Horrorsaurs, Sidesplitters, and many other creatures straight out of nightmares... We do not go in the jungle. We do not go in the jungle. We do not go in the jungle.
Should be fun....