The Noble Circle of Horrorterrors lead the mysterious eldritch creatures that reside in the Furthest Ring. These creatures seem to be getting massacred by an unknown source, later shown to be Lrd English, causing them to reach out to Sburb players. They whisper to the dreamers of Derse during the eclipse and have been seen enlisting Rose and Dave. They serve as a Derse player's advantage, equivalent to Skaian Clouds on Prospit. Feferi's Lusus, Gl'bgolyb, is referred to as an "emissary" to them.
They appear to have some sort of suspicious and mysterious agenda, but their involvement in Sburb remains unknown to this day. They seem to be opposed to the creation of new universes (although this may only apply to a universe created by the humans, which may or may not be linked with Lrd English, who is currently killing them off), but also to the complete destruction of reality. The horrorterrors are inspired by H. P. Lovecraft's Cthulhu mythos and are in fact referred to as Outer Gods at several points.
On Earth, the Squiddles are stated to be a subconscious re-imagining of the horrorterrors and other Beasts residing in the Furthest Ring, with the character Skipper Plumbthroat possibly representing Lrd English.
NRUB'YIGLITH, SHAMEBEAST KING OF GROTESQUERY, WRITHE-LORD OF THE MOIST BEYONDHOOD. Hearing his melodious chirps and tongue-clicks causes one's bones to explode.
It is possible that Nrub'yiglith is the kids' universes' version of Gl'bgolyb, existing somewhere within their universes. However, he may also dwell in the Furthest Ring, serving the Noble Circle of Horrorterrors and their underlings.
Oglogoth is found in Rose's Grimoire for Summoning the Zoologically Dubious. The Grimoire describes him as "OGLOGOTH, THE DEEP ONE". Whenever he grinds his teeth, all the children of a random galaxy somewhere will frown continuously for a nine thousand year span. He is the first and smallest of the SMALLER GODS, appointed in servitude of a vile, unfathomable pantheon of MIDDLING GODS which caters to the whims of the Noble Circle of Horrorterrors, an omniscient, omnipotent order of the elite few, forever cloaked in the darkness of the Furthest Ring."
He dwarfs Nrub'yiglith, who in turn looms over Fluthlu, so the scale of this creature is near unimaginable, and he is apparently the smallest of the smaller gods. Wow. Good thing the Grimoire is in the hands of a young lady with such a good head on her shoulders.
He is the patron of the fearsome Thorns of Oglogoth, which Rose obtains by combining her Needlewands and the Grimoire.
When a player goes to sleep after their dream self dies, they are free to come into close contact with the horrorterrors via the afterlife. Feferi, due to her positive connection with Gl'bgolyb, manages to talk them into "glubbing up" a series of stabilized dream bubbles that serve as a communication tool between the trolls and the kids, as well as the dead and the living.
Jack Noir and PM stand in awe by two wounded horrorterrors.
As Jack Noir and the prototyped Peregrine Mendicant flew through the Furthest Ring, they seem to be able to come into physical contact with the horrorterrors, but are either possibly unable to interact with them or too busy fighting to concern themselves with them.
On LOHAC, Rose was persuaded by Doc Scratch to ask the Magic Cue Ball if the horrorterrors were evil. The response was lines of meaningless incoherent text (except for the phrase "Oglog M'Rubbit," a callback to Problem Sleuth). Upon viewing this answer, she went Grimdark, an uncontrollable and horrifying process described as going "completely off the deep end in every way." This physically caused Rose to develop darkened skin, glowing eyes and a thorny black aura reminiscent of the horrorterrors' tentacles, and begin speaking in an incomprehensible language.
During her fight with Jack she seemed to be able to manifest her aura into actual physical thorns.
This can be interpreted as Rose losing control over the dark magic she received from the Circle. It could also be the result of a sudden surge of power granted her by the horrorterrors. Rose died shortly thereafter and was replaced by her dream self, yet the physical changes were not present on her dream self.
The word 'Grimdark' seems to have originated in the table-top game, Warhammer 40,000 and evolved into a memetic phrase.
It is currently speculated that a parallel to this power through the use of a combined cherub Juju is Trickster Mode, as seen when Janecaused a world-changing explosion and flew away shortly after engaging the transformation. While Rose's Grimdarkness is black, frightening, and out of control, Jane's Trickster Mode appears to be the exact opposite, being bright, silly, and even more so out of control. Also as Grimdarkness is "the fabled blackdeath trance of the woegothics" Trickster Mode is called "fabled peachbirth trance of the jokebollocks".
Andrew Hussie has frequentlyjokedthat thesessionthat created the Alternian universe was played by 48 Squiddles and that he shall reveal these characters and/or kill them soon. It should be noted that the Alternian universe has a 48 sign horoscope suggesting that the Sburb session that created it did indeed have 48 players, that The Ultimate Reward of Sburb is to create a new universe and then inhabit it whilst repopulating, and that Squiddles and horrorterrors are often treated synonymously (such as in Jade's dream, or Jane's trickster mode). Coincidentally, horrorterrors (sometimes addressed as gods) are, in fact, currently being killed off (by Lrd English). However, whether the horrorterrors are the previous players (or the offspring of those players) and creators of the Alternian universe or simply game constructs like denizens and carapaces is yet to be seen.