Horrorterror

The leaders of the mysterious eldritch creatures that reside in the Furthest Ring. They whisper to the dreamers of Derse, including Rose and Dave, and probably Sollux, Nepeta, Equius, Eridan, and Feferi, and serve as a Dersite version of the Skaian dream clouds. Feferi's lusus, Gl'Bgolyb, is an emissary to them. They have some sort of mysterious agenda, but their involvement in Sburb remains unknown.

When a player goes to sleep after their Dream Self dies they appear to come into close contact with the Circle. So far, we have seen this happen to Karkat, Jade, and Feferi. Karkat and Jade found the experience profoundly disturbing. Both were unusually agitated and moody after awakening, and insisted that they would never go to sleep again. However, the experience did not seem to cause any (additional) mental instability or lasting harm. Feferi, perhaps due to her positive experiences with her terrifying Lusus, didn't expect to be upset by seeing the Circle, and indeed was not at all bothered by the experience.

They seem to be getting massacred by something (Bec Noir?) and reach out to Rose and Dave's dreams to ask for help, as well as manipulating everyone who goes to sleep with a dead dream self.

They are most likely based upon the Great Old Ones and Outer Gods of H.P. Lovecraft's Cthulhu Mythos and Dream Cycle.