The Great Old One Crom-Cruach is believed to be related to Shudde M'ell. However it is unclear whether it is a Cthonian of huge size, or a unique entity.
Few Mythos tomes, with the exception of an obscure passage in Prinn's De Vermiis Mysteris where it is mentioned as "From beneath it devours".
Worship of the Great Old One was largely restricted to a few Druidic sects in the region of Fife, where various sacrifical barrows were marked with a spiral symbol. Victims were left tethered to sacrifical altars for Crom-Cruach to devour through various feeding tendrils, giving it the name "The Thousand Maws".
The Great Old One actually resides far beneath the Longannet area of Fife, where it is tended by a tiny human cult. Since the Night of the Worm, it is believed that the Great Old One is dead - however, Section 13 Telepaths have picked faint emanations from something beneath the Longannet fields...