Here is my Disciple of The Cult of the Sump Mother and entry for the Yakcomp 39: "Secret Society”.
At the very bottom of the Hive City, below the underhive lies the Sump. All scum and waste, be it living or matter eventually filters down to these dark depths of depravity.
The Cult of the Sump Mother was once a cult that worshiped the Hive’s Sump as a living profane god.
What these worshipers didn’t realise was that they were deceived by Chaos and what they thought were the miracles of the Sump Mother were actually the workings of Grandfather Nurgle.
Slowly these worshipers succumb to the taint of Nurgle and they became undying and free from pain as they let pestilence and decay ravage and fill their bodies and minds, all believing that it was the miracle of the Sump Mother.
There lies an area deep within the Sump that has become a a place of worship for the Cult. A garden of pestilence and decay that reflects that of their true god and master, the Lord of Pestilence. Fungi and Algae grown from rotten flesh and rivers of rot and muck fill the landscape with such vibrant yet deadly colour.
Here is a Disciple of the Cult of the Sump Mother trudging through the rotting swamps of this pestilent garden. Lichen and dodder growing out of his rotting flesh. Lifeless eyes glowing with disease. An old, corroded chain glaive held tightly in his decaying fingers. An old gas mask once worn to protect him from noxious gasses now fused to his very skin. And as a last gift from Nurgle, septic antlers grow from his back like a set of skeletal wings.