Source: Lords of Chaos, Book of the Damned Volume 2, pg(s). 41
Located deep within the Abyss, Yad Iagnoth is the name of the Abyssal realm thought to act as the main gateway to the qlippoth territories in the Abyss: such a dangerous place is claimed by no power at the moment.
Yad Iagnoth is situated as the highest of the deep Abyssal realms where the qlippoth still rule after having been cast down by the demons. Portals to these deeper realms are concealed in innumerable voids and crevices throughout Yad Iagnoth.
Much of Yad Iagnoth is composed of quasi-formless flesh and slime where fanged pits and pockets of poisonous gas might suddenly appear and vanish to prey upon intruders. Hideous fleshy structures, where qlippoth nest, rise from the ground or hang unsupported in mid-air; the largest such structures damage the fabric of the plane itself, opening holes to other planes. One of them leads to the nation of Tianjing in Golarion, through which the qlippoth led an invasion millennia ago but were repelled by a celestial host.
Cyclopean black stone pillars are scattered throughout Yad Iagnoth, each carved with ever-changing qlippoth runes. They are toxic to those nearby and warp the laws of nature in contradictory ways. Rare ancient tomes claim that these pillars contain treasures beyond the skill of mortals to create, but few treasure seekers return uncorrupted. Cancerous swamps and seas form in the most deliquescent parts of Yad Iagnoth, whose fluids are thick with intestinal tendrils.
At the centre of Yad Iagnoth, lies the Vast Scar, an unimaginably gigantic pit filled with a swirling, hypnotic darkness. The ascended qlippoth lord Rovagug left this mark behind when he gnawed his way out of the deepest Abyss to destroy the Great Beyond. The darkness that infests the pit is oily and semi-sentient, and beings who gaze into it quickly fall under its influence. It shares the exact shape and breadth as the Pit of Gormuz in Golarion.
The black pillars of Yad Iagnoth are honeycombed with tunnels where gorgoros qlippoth live and welcome aspiring treasure hunters hungrily. Nyogoths detach themselves from the tendrils of Yad Iagnoth's seas, roam the landscape, and consume intruders and other qlippoth alike. Elsewhere, especially in the caves and qlippoth nests, vast fungal masses swell and attempt to infect intruders with gushing spores or send these spores through new blistering wounds, giving rise to cythnigots.
Thulgants build towering colonies within Yad Iagnoth and fill them with petrified or preserved victims and bound servants. Many thulgants employ utukkus to draw in victims. Mortals are fit only as prisoners, slaves, or victims, and the choice is the thulgant's to make.