Shellfiends

The Shellfiends – Dwellers of the Abyss 
Lurking in the darkened waters where the ocean floor crumbles into the abyss, the Shellfiends are a nightmarish fusion of human intelligence and deep-sea monstrosity. These creatures are cunning, carnivorous, and utterly relentless, feared by sailors and coastal tribes alike. With the upper body of a gaunt, hairless humanoid and the lower half of a massive octopus, they glide through the depths, their long, sinewy tentacles propelling them with eerie grace. 
But their most distinctive feature is the colossal, jagged seashell they carry on their backs. A mobile fortress they retreat into when threatened, much like hermit crabs. These shells, often adorned with the skulls and bones of their victims, serve both as protection and as a chilling warning to those who might challenge them.