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 that is nonmagical
Condition Immunities charmed, exhaustion, frightened, poisoned
Senses truesight 120 ft., passive Perception 22
Languages all, telepathy 120 ft.
Challenge 24 (62000 XP)
Shapechanger.
Innate Spellcasting.
Legendary Resistance (3/Day).
Magic Resistance.
Magic Weapons.
ACTIONS
Multiattack.
Wave of Sorrow (Greatsword).
Teleport.
LEGENDARY ACTIONS
Attack.
Dance, My Puppet.
Sow Discord.
Teleport.

This full creature's stat block is not available (not OGL).

The appearance of the Dark Prince is a warning that not all beautiful things are good.
Mordenkainen´s Tome of Foes
Graz'zt