Aucturn is a Great Old One created by Paizo Inc for the Pathfinder RPG in 2007. It is in Paizo Inc's Starfinder RPG that Aucturn has been fully developed.
Aucturn, the Stranger is a newly born or created Great Old One. It's a living planet with an inhospitable geography, one that is mutable. Landmasses consist of chalky stone or rubber soil from which stunted, mutated vegetation grows. Unseen leviathans swim through the black sludge of its oceans. The atmosphere consists of poisonous gases, which vary depending on the place, from clinging soupy neurotoxin in one area to a thin hallucinogenic mist at another. From it's yellow sky, acidic rain pours on the land. It's geography is in a state of flux, morphing and twisting as the planet heaves and contracts. Rivers are drained and mountain ranges of flesh-like hummocks are created. Usually these changes happen over months or years, but sometimes they occur within moments.
Most of the planet's lifeforms are both vicious and monstrous, which include Shoggoth and Gugs. The most common lifeform are the orocorans, semi-intelligent predators. Considered by most to be nuisances, which pose a threat when assembled into large swarms. On the planet, there is an ongoing feud between the followers of the Outer Gods who dominate the world and the scattered cells of the Dominion of the Black. It's a lawless place, where evil runs rampant. Among the world's residents, no topic of study is forbidden and no act is taboo. Great factories produce illegal drugs outside of the reach of the law, revolutionaries plot against the governments of their homeworlds, slavery is common, and scholars research the forbidden arts so they can warp reality. The unofficial leader of Aucturn is the mysterious Carsai the King, whom is suspected of being an avatar of Nyarlathotep