Innate Spellcasting. Fraz-Urb'luu's spellcasting ability is Charisma (spell save DC 24). Demogorgon can innately cast the following spells, requiring no material components:
Legendary Resistance (4/Day). If Fraz-Urb'luu fails a saving throw, he can choose to succeed instead. Demonic Awakening (Recharges after a Short or Long Rest). If Fraz-Urb'luu would be reduced to 0 hit points, his current hit point total instead resets to 318 (80% of his maximum hit points) hit points, he regains any expended uses of Legendary Resistance. Additionally, he can now use the options in the "Mythic Actions" section for 1 hour. Magic Resistance. Fraz-Urb'luu has advantage on saving throws against spells and other magical effects. Magic Weapons. Fraz-Urb'luu's weapon attacks are magical. Undetectable. Fraz-Urb'luu can't be targeted by divination magic, perceived through magical scrying sensors, or detected by abilities that sense demons or fiends.
Multiattack. Fraz-Urb'luu makes three attacks: one with his bite and two with his fists. Bite. Melee Weapon Attack: +17 to hit, reach 10 ft., one target. Hit: 19 (3d6 + 9) piercing damage. Fist. Melee Weapon Attack: +17 to hit, reach 10 ft., one target. Hit: 22 (3d8 + 9) bludgeoning damage.
Conjure Walls and Doors. Fraz-Urb'luu causes up to 1d12 doors within 300 ft of him to become walls, and an equal number of doors to appear on walls where there previously were none. Fraz-Urb'luu needn't see the doors and walls, but he must aware of the doors and walls. Simulacrum. Fraz-Urb'luu chooses one humanoid he can see and instantly creates a simulacrum of that creature (as if created with the simulacrum spell). This simulacrum obeys Fraz-Urb'luu's commands and is destroyed at the start of his next turn. Psychic Anguish. Fraz-Urb'luu creates a wave of anguish. Each creature he can see within 120ft must succeed on a DC 24 Wisdom saving throw or take 33 ( 6d10) psychic damage.
Fraz-Urb'luu 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. Fraz-Urb'luu regains spent legendary actions at the start of his turn. Tail. Melee Weapon Attack: +17 to hit, reach 15 ft., one target. Hit: 20 (2d10 + 9) bludgeoning damage. If the target is a Large or smaller creature, it is also grappled (escape DC 25). The grappled creature is also restrained. Fraz-Urb'luu can grapple only one creature with his tail at a time. Phantasmal Killer (Costs 2 Actions). Fraz-Urb'luu casts phantasmal killer, no concentration required.
On Initiative count 20 (losing initiative ties), Fraz-Urb'luu can take a lair action to cause one of the following effects: he can't use the same effect two rounds in a row:
Fraz-Urb'luu's Lair is the city Zoragmelok.