Ari Nebarius, Lord of the Masquerade

Fey Sovereign: Ari automatically knows when he is lied to.

Illusion Mastery: Ari can see through illusions, invisibility, and magical darkness.

Legendary Resistance (3/day): If Ari fails a save, he can choose to succeed instead

Innate Spellcasting (Charisma). Ari Nebarius is a 20th-level spellcaster. Its spellcasting ability is Charisma (spell save DC 23, +15 to hit with spell attacks). Ari Nebarius has following spells prepared:
Cantrips (at will): Prestidigitation, Thaumaturgy, Minor Illusion, Mage Hand, Message, Eldritch Blast
1st level (4 slots): Charm Person, Disguise Self, Shield, Faerie Fire
2nd level (3 slots): Mirror Image, Misty Step, Detect Thoughts
3rd level (3 slots): Counterspell, Dispel Magic, Hypnotic Pattern
4th level (3 slots): Greater Invisibility, Phantasmal Killer, Wall of Fire
5th level (2 slots): Dominate Person, Wall of Force
6th level (2 slots): Mass Suggestion, Disintegrate
7th level (2 slots): Forcecage, Plane Shift
8th level (1 slot): Feeblemind, Maze
9th level (1 slot): True Polymorph, Power Word Kill

Action Name. Enter the description for your action.

Masquerade Rapier. Melee Weapon Attack: +13 to hit, reach 5 ft., 1 target. Hit: 14 (2d8 + 5) piercing damage plus 18 (4d8) psychic damage.

Fey Charm (Recharge 5-6). Ari targets one creature he can see within 60 feet. The target must succeed on a DC 23 Wisdom saving throw or be charmed for 1 minute. While charmed, the creature regards Ari as its beloved and will defend him.

Illusory Duplicate (Recharge 4-6). Ari creates 1d4 illusory copies of himself (like Mirror Image, but they can appear anywhere within 30 ft. of him).

Fey Step. Ari teleports up to 30 feet. He can leave behind an illusion of himself that lasts until the start of his next turn.

Taunting Word. Choose a creature within 60 feet. It must make a DC 23 Wisdom saving throw or have disadvantage on attacks against creatures other than Ari until the end of its next turn.

Mask of Mirrors. When targeted by an attack, Ari can force the attacker to make a DC 23 Wisdom save or attack themselves or another creature within reach instead.

Ari can use 3 legendary actions, choosing from the options below. Only one legendary action can be used at a time.

Dance of Blades (Costs 1 Action). Ari makes a rapier attack

Dispel Trickery (Costs 1 Action). Ari snaps his fingers, automatically dispelling one illusion, invisibility, or magical darkness effect within 60 feet.

Command the Court (Costs 1 Action). Ari summons 1 Satyr, 1 Redcap, or 1 Blink Dog into the fray (once per round).

Glamour Step (Costs 2 Actions). Ari teleports 30 ft. and creates an illusion of himself at the original spot.

(Use if party dispatches Ari with ease)

Masquerade Incarnate (Recharges after a Long Rest). When Ari is reduced to 0 hit points in his lair, he doesn’t die. Instead, his body shatters into a storm of rose petals, masks, and thorned vines. At the start of his next turn, he reforms in a terrifying, unmasked Fey Lord form with half his hit points restored. All conditions and effects on him end.

While in this form, Ari gains the following benefits:

• Immune to radiant and necrotic damage.

• His melee and spell attacks deal an additional 2d8 psychic damage.

• He can take Mythic Actions in addition to his Legendary Actions.

Mythic Actions

Ari can take 3 mythic actions, choosing from the options below. Only one mythic action can be used at a time and only at the end of another creature’s turn.

• Shatter Mask. (Costs 1 Action) Ari causes all illusions within 60 feet (including those not of his making) to collapse violently. Each creature of his choice in that area takes 18 (4d8) psychic damage and must succeed on a DC 23 Intelligence saving throw or be blinded until the end of its next turn.

• Thorn Cage. (Costs 1 Action) Ari targets one creature he can see within 60 feet. The target must succeed on a DC 23 Strength saving throw or become restrained as thorned vines erupt around them. While restrained this way, the creature takes 14 (4d6) piercing damage at the start of its turn. The target can repeat the save at the end of each of its turns, ending the effect on itself on a success.

• Dance of Madness. (Costs 2 Actions) Ari unleashes a wave of Fey glamour. Each creature of his choice within 30 feet must succeed on a DC 23 Wisdom saving throw or immediately use its reaction (if available) to move up to its speed and make one weapon attack against a random adjacent creature.