Graz'zt

From Mordenkainen's Tome of Foes, page 149.

Graz'zt
Large fiend (demon, shapechanger), chaotic evil
Armor Class: 20 (natural armor) Hit Points: 346 (33d10 + 165) Speed: 40 ft.
STR 22 (+6)	DEX 15 (+2)	CON 21 (+5)	INT 23 (+6)	WIS 21 (+5)	CHA 26 (+8)
Saving Throws: Dex +9, Con +12, Wis +12 Skills: Deception +15, Insight +12, Perception +12, Persuasion +15 Damage Resistances: cold, fire, lightning Damage Immunities: poison; bludgeoning, piercing, and slashing from nonmagical attacks Condition Immunities: charmed, exhaustion, frightened, poisoned Senses: truesight 120 ft., passive Perception 22 Languages: all, telepathy 120 ft. Challenge Rating: 24 (62,000 XP)
Innate Spellcasting. Graz'zt's spellcasting ability is Charisma (spell save DC 23). He can innately cast the following spells, requiring no material components: At will: Charm Person, Crown of Madness, Detect Magic, Dispel Magic, Dissonant Whispers 3/day each: Counterspell, Darkness, Dominate Person, Sanctuary, Telekinesis, Teleport 1/day each: Dominate Monster, Greater Invisibility Legendary Resistance (3/Day). If Graz'zt fails a saving throw, he can choose to succeed instead. Magic Resistance. Graz'zt has advantage on saving throws against spells and other magical effects. Magic Weapons. Graz'zt's weapon attacks are magical. Shapechanger. Graz'zt can use his action to polymorph into a form that resembles a Medium humanoid, or back into his true form. Aside from his size, his statistics are the same in each form. Any equipment he is wearing or carrying isn't transformed.
Actions
Multiattack. Graz'zt attacks twice with Wave of Sorrow. Wave of Sorrow (Greatsword). Melee Weapon Attack: +13 to hit, reach 10 ft., one target. Hit: 20 (4d6 + 6) slashing damage plus 10 (3d6) acid damage. Teleport. Graz'zt magically teleports, along with any equipment he is wearing or carrying, up to 120 feet to an unoccupied space he can see.
Legendary Actions
Graz'zt can take 3 legendary actions, choosing from the options below. Only one legendary action can be used at a time and only at the end of another creature's turn. Graz'zt regains spent legendary actions at the start of its turn. Attack. Graz'zt attacks once with Wave of Sorrow. Dance, My Puppet. One creature charmed by Graz'zt that Graz'zt can see must use its reaction to move up to its speed as Graz'zt directs. Sow Discord. Graz'zt casts Crown of Madness or Dissonant Whispers.
Lair Actions
On Initiative count 20 (losing initiative ties), Graz'zt can take a lair action to cause one of the following effects; he can't use the same effect two rounds in a row: Graz'zt casts the Command spell on every creature of his choice in the lair. He needn't see each one, but he must be aware that an individual is in the lair to target that creature. He issues the same command to all the targets. Smooth surfaces within the lair become as reflective as a polished mirror. Until a different lair action is used, creatures within the lair have disadvantage on Dexterity (Stealth) checks made to hide.
Regional Effects
The region containing Graz'zt's lair is warped by his magic, creating one or more of the following effects: Flat surfaces within 1 mile of the lair that are made of stone or metal become highly reflective, as though polished to a shine. These surfaces become supernaturally mirrorlike. Wild beasts within 6 miles of the lair break into frequent conflicts and coupling, mirroring the behavior that occurs during their mating seasons. If a humanoid spends at least 1 hour within 1 mile of the lair, that creature must succeed on a DC 23 Wisdom saving throw or descend into a madness determined by the Madness of Graz'zt table. A creature that succeeds on this saving throw can't be affected by this regional effect again for 24 hours. If Graz'zt dies, these effects fade over the course of 1d10 days.
Madness of Graz'zt
If a creature goes mad in Graz'zt's lair or within line of sight of the demon lord, roll on the Madness of Graz'zt table to determine the nature of the madness, which is a character flaw that lasts until cured. d100 Flaw (lasts until cured) 01-20 "There is nothing in the world more important than me and my desires." 21-40 "Anyone who doesn't do exactly what I say doesn't deserve to live." 41-60 "Mine is the path of redemption. Anyone who says otherwise is intentionally misleading you." 61-80 "I will not rest until I have made someone else mine, and doing so is more important to me than my own life — or the lives of others." 81-90 "My own pleasure is of paramount importance. Everything else, including social graces, is a triviality." 91-00 "Anything that can bring me happiness should be enjoyed immediately. There is no point to saving anything pleasurable for later."