Yeenoghu, the Beast of Butchery

Innate Spellcasting. Yeenoghu’s spellcasting ability is Charisma (spell save DC 21, +13 to hit with spell attacks). He can innately cast the following spells, requiring no material components:

At will: detect magic, spiritual weapon (8th-level spell, 4d8 + 5 force damage on a hit, appears as a flail)

3/day each: dispel magic, fear, invisibility

1/day each: teleport

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.

Magic Weapons. Yeenoghu’s weapon attacks are magical.

Rampage. When Yeenoghu reduces a creature to 0 hit points with a melee attack on his turn, Yeenoghu can take a bonus action to move up to half his speed and make a bite attack.

Essence of Demogorgon. Yeenoghu has 4 canisters of black ichor connected to him. If these canisters are destroyed, certain aspects of his defenses will be lowered. If 1 canister is destroyed, his AC is lowered by 2. If 2 canisters are destroyed, he loses his resistance to magical physical damage and force damage as well as his magic resistance. If 3 canisters are destroyed, he is affected by the slow spell. If all 4 canisters are destroyed, he has a 25% chance of being affected by the confusion spell. Each canister has an AC of 18, has 30 hit points, and is immune to psychic, poison, and necrotic damage.

Should a canister or multiple canisters remain, depending on the number of canisters when Yeenoghu reaches 120 hit points or less, he will enter a battle rage, granting himself buffs. If one canister remains he will no longer be under the effect of the slow spell and his AC will return to 22. If 2 canisters remain he will also gain proficiency in all saving throws, but lose any remaining uses of Legendary Resistance. If 3 canisters remain he also gains the effects of the haste spell, not requiring concentration. If all 4 canisters remain, each ability score increases by 5.

Multiattack. Yeenoghu makes three flail attacks. If an attack hits, he can cause it to create an additional effect of his choice or at random (each effect can be used only once per Multiattack):

1. The attack deals an extra 13 (2d12) bludgeoning damage.

2. The target must succeed on a DC 21 Constitution saving throw or be paralyzed until the start of Yeenoghu’s next turn.

3. The target must succeed on a DC 21 Wisdom saving throw or be affected by the confusion spell until the start of Yeenoghu’s next turn.

Three Headed Flail. Melee Weapon Attack: +12 to hit, reach 15 ft., one target. Hit: 32 (2d12 + 19) bludgeoning damage.

Bite. Melee Weapon Attack: +17 to hit, reach 10 ft., one target. Hit: 14 (1d10 + 9) piercing damage.

Claw. Melee Weapon Attack: +17 to hit, reach 15 ft., one target. Hit: 20 (3d6 +9) slashing damage.

Yeenoghu can take 3 legendary actions, choosing from the options below. Only one legendary action option can be used at a time and only at the end of another creature’s turn. Yeenoghu regains spent legendary actions at the start of his turn.

Charge. Yeenoghu moves up to his speed.

Swat Away. Yeenoghu makes a flail attack. If the attack hits, the target must succeed on a DC 25 Strength saving throw or be pushed 15 feet in a straight line away from Yeenoghu. If the saving throw fails by 5 or more, the target falls prone.

Savage (Costs 2 Actions). Yeenoghu makes a bite attack against each creature within 10 feet of him.