Legendary Resistance (3/Day). If Yeenoghu fails a saving throw, he can choose to succeed instead.
Magic Resistance. Yeenoghu has advantage on saving throws against spells and other magical effects.
Spellcasting. Yeenoghu casts one of the following spells, requiring no material components and using Charisma as the spellcasting ability (spell save DC 17):
At will: detect magic
1/day: teleport
3/day each: dispel magic, fear, invisibility
Multiattack. Yeenoghu makes three Flail attacks.
Flail. Melee Weapon Attack: +16 to hit, reach 15 ft., one target. Hit:22 (2d12 + 9) force damage. If it's his turn, Yeenoghu can cause the target to suffer one of the following additional effects, each of which he can apply only once per turn
Bite. Melee Weapon Attack: +16 to hit, reach 10 ft., one target. Hit:20 (2d10 + 9) acid damage.
Rampage. When Yeenoghu reduces a creature to 0 hit points with a melee attack, he moves up to half his speed and makes one Bite attack.
Charge. Yeenoghu moves up to his speed.
Swat Away. Yeenoghu makes one Flail attack. If the attack hits, the target must succeed on a DC 24 Strength saving throw or be pushed up to 15 feet in a straight line away from Yeenoghu. If the saving throw fails by 5 or more, the target is also knocked prone.
Savage (Costs 2 Actions). Yeenoghu makes a separate Bite attack against each creature within 10 feet of him.
The Beast of Butchery appears as a great scarred gnoll, towering 14 feet tall. Yeenoghu is the Gnoll Lord, and his creations are made in his twisted image. When the demon lord hunted across the Material Plane, packs of hyenas followed in his wake, and those that ate of great Yeenoghu's kills became gnolls. Few others worship the Beast of Butchery, but those who do tend to take on a gnoll-like aspect, hunching over and filing their teeth down to points.