Ghouls are, in their own way, a significantly more benign race than humanity. They are a violent, ruthless, carnivorous race, but they are also erudite and cultured. Ghouls also are pragmatic in a way humans aren't with conflicts among them usually settled one-to-one or the application of the Law of Mordiggian and Wisdom of Tsathougghua. Which summarized quickly mean that the rights of individuals are always subservient to the pack and those who endanger the pack are slaughtered then eaten. It also teaches one shouldn't start a fight but always finish it.
With the exception of the fact eating the fallen is a commonly accepted practice, their causal use of magic mixed with technology, and their worship of the Great Old Ones, it is entirely possible for human beings to live with ghouls in a way which would not drive them insane. Indeed, many ghoul cities have as much as 10% of a human population.
Ghoul society simply comes off as a society which is absolute in certain laws and very communally organized. As long as one abides by one's word and the laws absolutely, it is perhaps one of the safest places to live in the Wasteland. Not purely safe, mind you, but not so far from existing human cultures today.Albeit these are often mutated and able to digest the flesh of their kin. These albino, goggles-wearing individuals tend to be known as Morlocks despite the fact H.G. Wells based his fictional creations on a chance encounter with a ghoul in the London Underground.
The ghouls have not always been as pleasant as they are in the 22nd century. Many of their past cities included feral ones where humans were raised like cattle, used as slaves, or eaten. Violence was a common display and sacrifices were a common display. Even worse, according to ghouls, they warred upon one another and allied with things like Ghasts or Gugs.For better or worse.
The shift in ghoul culture took place when the Great Old One Mordiggian appeared unto them and passed upon them the laws of their kind. Later, a time-travelling Randolph Carter brought his childhood friend Richard Pickman with him who taught them The Changeling Way where human children were exchanged with ghoul ones. This horrible practice taught them to appreciate humans as equals, even if they never lost their taste for them. Indeed, solely among the Mythos are humans considered such by a Servitor Race.
The existence of Changelings led to the ghouls developing a process for humans to become part of their race, to interbreed back with them, and also to share the gift. This led to the legends of lycanthropy, skin-dancing, and other stories. Not all humans reacted well to this transformation and many ghouls which were not able to make contact with their fellows and were raised exclusively by humans became dominated by their hunger.Mordiggan like most of the Hyperborian Great Old Ones are less powerful than the rest of their kin but curiously willing to interact with lesser beings, even if they view it more like gardening with ideas than discussion.
Modern warfare eventually drew the ghouls back to the surface as their carnivorous race was always short of meat and their presence was noted in the Civil War, World War 1, World War 2, and in the various camps of Joseph Stalin. Stalin apparently discovered the truth of ghoul infiltration of his people for "food" but his body disappeared only to be replaced with a fake soon after.Historical French werewolf Peter Stumbb, notably because a cult to Nyarlathotep who he identified with Satan and other Great Old Ones which passed the knowledge of the ghouls liberally onto their followers, creating many cannibal cults of humans.
The United States became aware of the ghoul "threat" in the 1950s and used underground military tests to attack their races. This proved to be a mistake on their part as many humans were dragged to their horrific demise as a result. Worse, the ghouls demonstrated their ability to create earthquakes and other disasters which would destroy the country outright.
The devastation of the Rising killed almost half of the ghoul race and collapsed countless caverns. Many ghouls have since fled to the surface where they have begun building scrap-yard cities from the junk of humankind's refuse. In general, ghouls work well with larger populations of humans which will have them but their treatment at the hands of many have also turned others to the Old Ways. Others have turned completely feral and lost their cultured nature. These ghouls live like the animals their instincts tell them to be and hunt humans like bipedal wolves.Wiser individuals sought the knowledge of the ghouls for its own sake. This included knowledge of oil and other resources as well as technologies we now take for granted today. British sorcerer Alan Turing was actually friendly with two fellow ghoul-human hybrids working at his facility who enlightened him to numerous secrets of the Mythos before going to live with them--albeit that is contradictory to the idea he left for Yith.
Powers: Ghouls are generally far stronger than normal human beings as well as far more durable. They receive a +4 to Strength and +2 Constitution as well as a +1 to their Dexterity score. Humans find ghouls horrifying and they are also generally pack creatures who do not engage in double-talk or fancy words, which results in conversations being very difficult persuasion wise. This gives them a -2 to their charisma and a minus 4 if humans can't get past their horrifying visages.
Hybrids have a +2 to their Strength score and -1 to their Charisma due to the difficulty of disguising the predator within. Eventually, hybrids transform themselves into complete ghouls. Ghoul claws are excellent for both digging as well as slashing and inflict a +2 Strike Damage with the same for their teeth. Ghouls do not age after adulthood and some of their elders are as old as the Hyborean Age.
Ghouls are Dreamers equal to humanity and have far greater use of magic among them. They are also accomplished scientists, easily blending sorcery and technology.
Roleplaying Hints: Ghouls are like Serpent Men in that it is entirely possible to hold lengthy conversations about human-related subjects with them without the subjects devolving into things like how much they want to eat you (albeit that's not off the conversation list). Generally, a ghouls word is his bond in a manner that he would be quite offended to assume he does not mean exactly what he says with no exaggeration. This also means ghouls are very good bargainers and do not appreciate double talk. Strangely, they are amazing storytellers but draw a distinction between "Dream Stories" and "Ground" stories.
Ghouls have a somewhat gamer-esque view of violence with no taboo against eliminating threats and utter ruthlessness against enemies. They also do not generally hold grudges provided a subject has shown he is no longer an enemy. They are also a carnivorous people, which means that food is always a source of concern for them and an acceptable payment. They also often bargain for human entertainment (high and low) as they consider us a very artistic race and one of the few which equals them.
Feral Ghouls are none of this and can be summarized as "HISS, ATTACK."