The Spawn of Yog-Sothoth are a fictional race created by Chaosium in 1994 for the Call of Cthulhu RPG, which were based on Lovecraft's Dunwich Horror.
The Spawn of Yog-Sothoth are mindless squirming masses of flesh which exude an indescribable monstrous stench. They have a weak form of invisibility and are immune to both cold and fire. They quickly grow to large size, and if they continue to feed, will continue to grow but at a much slower rate. Really old Spawn of Yog-Sothoth are the size of buildings or small hills. If killed, their flesh rapidly melts and soon only a crusty stain remains.