The Dwellers in the Depths are a fictional race created by Chaosium in 1994 for its Call of Cthulhu RPG, which were based on Ramsey Campbell's The Horror from the Bridge.
Dwellers in the Depths are amphibious creatures that serve the Great Old Ones, usually those associated with water. Whom are theorized to be Deep Ones, a mutant strain that is larger, more powerful, and possesses tentacles.
They live in their underwater cities, occasionally coming to the surface to feed and wreck havoc. Their semi-gelatinous rubbery flesh is immune to most types of physical attacks, and if slain quickly decompose, leaving a foul smelling stain.