"Little People" of Leng

There's too many weird peoples in the Mythos who all kind of "mean" the same thing. Some judicious pruning for importation into DFX is... well, judicious. The following three "races" of subhumans can all be combined into a single group, instead of three separate ones.

• The "Little People", also known as the Worms of the Earth (from the story of the same name by Robert E. Howard) and several other REH stories. They seem to also be the same people that he refers to in "People of the Dark" and "The Children of the Night" as well as (probably) "The Black Stone." These guys also may be the same, or meant to be referring to the same beings as mentioned by Lovecraft briefly in "The Whisperer in Darkness" and Arthur Maachen's "The Novel of the Black Seal." They don't seem to have a common name, other than perhaps the Worms of the Earth themselves, but they are described the same way in all cases. 
• The Tcho-tcho (and possibly also the tchortcha) mentioned in "The Horror at the Museum" as well as being a major component of the T.E.D. Klein story "Black Man With a Horn" (highly recommended, by the way.) These guys are more human-like, perhaps, than the Worms, or at least they seem to be be able to pass as an unsettling and alien human race whereas REH always describes the Worms as subhuman, but their cannibalistic tendencies alone make them horrifying. 
• The satyr-like "Men of Leng" which are most prominently featured in The DreamQuest of Unknown Kadath both in their native environment on Leng and as the black galley sailors that come to Dylath-Leen with weird moon rubies, and who take slaves from the lands of men. 

Honestly, conceptually all of these people are similar to my own Wendaks or Grendlings; the Children of Grendel, the Lingering Atlanteans; in that they are an ancient, subhuman (and devolving even more as time goes on) race that is on the outs, hostile to humanity, and kind of horrifying. Maybe I can simply use the race that I already have, but borrow elements (as needed/desired) from the races above. In particular, I like the fact that they live in very remote places, possibly even underground in very remote places to make them even more remote... but that lingering relics and ruins of their past worship of monsters like Tsathoggua, Ghoth the Burrower, Yogash the Ghoul, Chaugnar Faugn, Gol-goroth, Shugoran, or whomever. (REH specifically mentions Cthulhu and Dagon, I believe, too, in "Worms of the Earth".)

However, if I do that, and I'm leaning strongly towards so doing, I need to establish some kind of connection between the Grendlings and Leng that doesn't currently exist. For the remainder of this post, I'll be noodling with some ideas. 

First off, of course, it's worth level-setting; the Grendlings are degenerate and continuously degenerating descendants of Atlanteans who were on the main continent for whatever reason (mostly as soldiers, slaves or somesuch) when Atlantis sank. Although the curse of Atlantis still fell on them, they didn't (obviously) sink into the sea, since they weren't on Atlantis, so they didn't just drown in a watery cataclysm like the majority of their race. The curse that they inherited was, however, more insidious and delayed. I'm not sure how long ago Atlantis sank. A long time ago, but it doesn't have to be tens of thousands of years, or anything. The tendency of fantasy creators to overly prolong their timelines and histories into ridiculously long periods is unnecessary. Besides, if the curse still hasn't caught up to them after tens of thousands of years, it really wasn't all that terrible. I'm thinking the sinking of Atlantis can't be more than about a thousand years ago at most.

Secondly, Leng is much more ancient than Atlantis. Leng, like Amrruk the Ancient probably predates the world as we know it; it goes back to whatever pre-Adamite world existed here before it was wiped clean and reset with the current race of men.  The plateau of Leng is difficult to reach, nearly impossible to climb, and extremely uninviting, just from an environmental perspective.  Very little grows on its cold, windswept surface, which is littered with ancient menhirs, standing stones, and crumbling ruins of ancient walls and structures who's purpose can only be guessed at today.  The few creatures that eke out a living on the plateau of Leng are carnivorous giant spiders and cannibalistic Grendlings who are darker in nature, and more mystical and sorcerous than those who live in the Haunted Forest or Orlok Marshes, or other pockets of Grendling population.

Despite this, there appear to be other inhabitants of some kind as well.  Eerie howls of unknown provenance echo across the vast table-land, and the scratching and digging of some kind of creature that is rarely glimpsed but frequently heard can be picked out by keen listeners as well.  These glimpses seem to be of pale, lumpish creatures that are not even vaguely humanoid, being instead hunched, toad-like creatures, like Deep Ones who have lived for generations in caves and become pale and eyeless.

This bleakness is broken by a few landmarks:

Carcosa. Located on the edge of the plateau, with sheer cliffs that fall along with a tall, thin waterfall from the dark, silent waters of Lake Hali from which nearly constant mist rises, this abandoned and cursed city has no inhabitants that can be seen, but there is always an eerie feel of watchfulness and menace.  A strange flapping sound, as of rags hung out in a strong wind, echoes through the deserted stone.  According to patchy myths and legends, the King in Yellow himself might haunt Carcosa at times. Carcosa, apparently, predates the current age of mankind.

Sarkomand. A city of the Grendlings, where they have some measure of culture.  Ruled over by the Elder Heirophant (also known as the Tcho Tcho Lama, or the High Priest Not to Be Described), a mysterious figure who also hides himself behind yellow robes, this is a sinister city where peoples of the Three Realms might come as slaves—possibly—but they don't live long.  Rumors are that vast caverns called the Vaults of Zin lurk underneath the city.

Hsan. A city near the center of the plateau, peopled by carnivorous and intelligent (yet barbaric) hairy creatures (withered and emaciated ape-like carnivores called wijikos adapted to the cold, windswept environment on top of the plateau) They also have a subject relationship of sorts with the Heirophant, and provide many of the goods that the Heirophants people need to live—although they also have a fractious relationship, since the wijikos cannot live with anyone, and frequently bring violence to the people of Sarkomand and anyone else that they can reach. Exiled Grendlings do live among them, especially the most degenerated individuals, that are little more than apes themselves.

Atlantis apparently was enchanted by the ruins and eerie mystique of Leng, and heedless of the danger. They established an ancient city at its foot called Mnar, from which expeditions to Carcosa and elsewhere were launched. Although it's impossible to know now, it is likely that whatever the Atlanteans found on Leng was instrumental in their own degeneracy and cursing, and the destruction of their nation; a poison pill more thorough is hard to imagine.

The ruins of Mnar are known to seekers of esoteric and forbidden knowledge, but they are difficult to explore, as they are half buried in thick, viscous, mud and cold fens with reeking, tall grasses, thick although scattered trees, and near constant fog. Most believe that the entire area is haunted, and strange sounds are frequently heard when in the area, but there is no reliable information on what is actually there.