Kassogtha is a Great Old One of the expanded Mythos, created by Joseph S. Pulver Sr. for his 1999 novel Nightmare’s Disciple. She is told as Cthulhu’s sister and mate, and the mother of the twins Nctosa and Nctolhu. Her form is a ceaselessly writhing mass of tentacles, and she is also named the Coiled One and the Leviathan of Disease.
What defines Kassogtha is sickness itself. Like a parasitic disease she seeps into living things to corrupt and mutate them, and at times she merges her body with another entity, that union giving rise to new offspring. Creation and destruction as one act — it shares a register with our world’s motif of proliferation, the debt that swells as it spreads.