Yeenoghu is definitely a scheming manipulator.
A plane of the Abyss existed that was nothing but the rotting corpses of sentients drawn from other layers of the Abyss and the material plane as well. Like falling stars drawn towards a planetoid, the archetype of the sentient corpse drew its kind inward, and the plane fed and grew. In this plane the ghouls, maurezhi, and nabassu thrived. As this improved its status, the layer began to reward the devouring of its corpses, and in this environment one of the scavengers eventually emerged as a ruler. His name is represented as a primal laugh-howl: Yeenoghu. Ultimately, the demon lord was to dominate two layers, the 421st and 422nd: the White Kingdom and the Seeping Woods.
Like the hyaenadons, gnolls were often carrion eaters, and as Yeenoghu's power grew he noted this and determined the entire race would be his. Largely, he's succeeded, offering more power than the Laughing Father of the Hunt could, especially to the often disenfranchised males. With the power of Yeenoghu behind them, many male clerics or adepts have grown to dominate their tribes. The remaining worshippers of Gorellik treat their hyaenadons and dire lions better and eat carrion as a matter of mere convenience instead
of as a sacred imperative as Yeenoghu's followers do, and they tend to be more matriarchal. Where both Powers are revered, Yeenoghu is always more important, since his fading rival lacks the personality to inspire as much as he once did, while for the gnolls the demon prince's moon is waxing or full, still active and interested in mortal affairs.
For the cultists of Yeenoghu, the pursuit of more and more worthy carrion is the most holy act they can pursue. The grisly body parts Yeenoghuans use as trophies are scored with patterns of knife or tooth marks to indicate the corpse's previous status. Important and esepecially strong, intelligent, or charismatic people may be targeted so that they can be slain, buried, and eaten in ceremony, in Yeenoghu's name.
Yeenoghu desires to spread his dominion to all those who consume corpses, thereby cementing a continuous energy loop between himself, his plane, his servants, and cannibalistic necrophages everywhere. If everyone eats corpses, everyone will serve Yeenoghu. This is not yet a true statement; many, even among gnolls and ghouls, eat the occasional moldering corpse without being responsible to the hungering lord in any way. This is why Yeenoghu must have two goals: to encourage the consumption of sentient corpses among those who haven't tried them, and to conquer those who do so already.
Yeenoghu has cults among humans in isolated xenophobic communities, the lairs of strangely inbred families, and the filthy hearts of impoverished cities. Occasionally, as among the ghouls of Nehwon, an elder race of living creatures with transparent flesh, he'll gain dominion over entire city-states. Yeenoghu has cultists among many races with kinship to dogs, crows, vultures, wolves, worms, pigs, and swine. Often, in Yeenoghu-lead societies, the ancient leaders will be transformed into the undead form of ghouls to lead the community in blind hunger long after their reign should have ended. Gnolls and flinds generally reject this because the stench of ghoul or ghast flesh makes them too hungry to follow what they perceive as food, or to do anything but pounce. This creates a gap between Yeenoghu's two
major sets of followers that he has never been able to bridge. Gnolls who become ghouls must leave the clan to avoid being devoured by their former allies. Hungry gnolls will ignore the risk of paralysis for the sake of tasty undead meat.
Temples to Yeenoghu always contain a trophy room, as well as a filthy celler in which corpses can be allowed to age.
With the aid of his servants, Yeenoghu offers power with a price. The price is service to the Devourer of the Departed and an increasing urge to consume the deceased, an act which ultimately increases the power of Yeenoghu's layer of origin. The giggling tempters of the ghoul-king love to increase their victims' association of dead flesh with real rewards.
The demon-prince's method of seducing others into his sphere of influence works in stages. Initially, the Jackal sends a cultist to encourage the vulnerable. Yeenoghu's cult is strongest among the gnolls and flinds, but also exists wherever food is scarce and corpses are common. Yeenoghu seeks first to change his victims' dietary mores, then her habits, creating a
horrible addiction, and finally to use the addiction as leverage to control the addict or to convince the victim to commit evils in order to feed their urge.
Important and reluctant marks may earn a visit from a succubus, incubus, or glabrezu. Yeenoghu's tempter demons aren't particularly interested in sex: they use their charm and persuasion to push their victms toward fouler deeds. Through centuries of experience, they can be quite cunning, not just showing up with a "It's delicious, why don't you try it?" but manipulating events to create a perceived need to join the incubus in its favorite repast. The
succubus or incubus -- whispering demon -- tries to bind its victim with a psychological dependence on the tempter or one of Yeenoghu's cults, so much so that they are willing to do anything, anything to please their psychological center.
"Don't you love me? Do you really, really love me? Why can't you accept the need for this? Our need for this? Jamie doesn't need his body any more, and we need his spiritual strength to survive."
"But we killed him! We killed him and left his body to rot!"
"You killed him, honey. You did it for us."
Yeenoghu uses the lure of carrion to draw prize vrocks to himself, turning them into ghouls in all but name: rotting, rubbery, gibbering, slightly canine corpse-eating vrock armies to do Yeenoghu's will.
I think I'd start by doubling their "avatar" CR (38-46). Now you have a beast who might be able hold his throne for a while from the rank and file... 
