Yeenoghu (MToF)
Yeenoghu, The Beast of Butchery and Gnoll Lord, is the Demon Lord of slaughter and eating to an excessive degree. Despite the obvious parallel to gluttony, Yeenoghu maintains a powerful predatory form rather than the stereotypical portly frame you would find depicted on a creature that is constantly eating.
Despite being a Demon Lord dedicated to destruction, Yeenoghu is responsible for the creation of the Gnolls, who are his chosen way to influence the material world, though he also boasts a selection of loyal demons (some of which he also created). Other cultists are rare, and take on Gnoll-like traits, including the signature Rampage power and gaining the Gnashing Jaws attack (which should be considered a Bite attack for maximum synergy with Gnoll warbands), and most importantly, the “kill everything and eat it” mentality. Which is basically what all plots involving The Beast of Butchery devolve into.
That said, it would be interesting to see how PCs react to finding a young orphan who has become a Cultist of Yeenoghu (perhaps they did something horrible, like killing someone to make an escape, or ate some humanoid flesh in the presence of a Gnoll raid, and the Gnolls said “Kid, you are alright, come with us!”). Could they redeem such a person?
Speaking of cultists, you are going to need some backup when you run Yeenoghu. Both in order to maximize his powers, and to cover his weaknesses. Creating some higher CR gnoll backup is as easy as selecting an NPC and appending the Rampage trait and a Bite attack to them. His main problem will be dealing with Flying PCs so make sure that there are more than a few ways to knock them out of the sky. Keep in mind that Demons can also be cultists, so feel free to add Rampage to them too.
The Lord of Gnolls has his own lair, the Death Dells, which he largely treats as his own hunting grounds in order to play out The Most Dangerous Game. His lair actions largely serve to help his Gnoll and Hyena underlings, by granting them advantage or giving them speed boosts, but he can also spike someone to restrain them just long enough for the hunting pack to catch up.
As for his personal combat routine: At CR 24 (25 in his lair), Yeenoghu is a melee ground bound brute with a few control options. His multiattack allows him to attack with his signature flail, The Butcher, three times (presumably once with each head). Each of the heads of this flail have a different rider, two of them being control options, and the other extra damage. Paralysis is the most devastating option to be sure. Yeenoghu can also cast spells, but realistically (outside of using Invisibility to ambush) he would only use them if he had no other choice. Yeenoghu possesses the Rampage bonus action of the Gnolls, so if you are using some backup that can capitalize on that you should. His legendary actions are very basic: Move, attack (with some control), and AoE attack.
Once again, I have to stress that Yeenoghu needs backup to perform at his best. Don’t send him out without an entourage.
In the Changeover, Yeenoghu lost his madness table. He gained immunity to all non magical B/P/S, which makes him immune to fall damage. He lost the Spiritual Weapon spell, and had the damage on his other attacks bumped up a bit. I have to say it took me a moment to parse the new formatting on his Flail. Previously it was a numbered list, which made it easy to interpret as a subfeature of the attack. Currently, the numbers were replaced with bolded names, which make them look like separate actions in the new format.
