Gargauth, The Tenth Lord of Nine

Enthralling Aura. Any creature that starts its turn within 20 feet of Gargauth must make a DC 24 Wisdom saving throw, unless Gargauth is incapacitated. Unless the save succeeds, the creature is charmed for 1 hour, or until Gargauth does anything harmful to the target. Although the target isn’t under Gargauth’s control, it takes the Tenth Lord of Nine’s requests or actions in the most favorable way it can, and willingly becomes the target of Gargauth's obsession spell (automatically fails the save). Effects that would normally end the charmed condition (such as greater restoration) instead allow the target a new saving throw. If a creature’s saving throw is successful, the creature is immune to Gargauth’s Enthralling Aura for the next hour. 

Shapechanger. Gargauth can use its action to transform into a Medium humanoid (most often a tall, mustached human or tiefling of handsome and noble visage), or back into his true form. His statistics remain the same. Any equipment he is wearing or carrying isn't transformed. If he dies, he reforms elsewhere in the multiverse in his true form due to his Immortal Nature (see Description).

Innate Spellcasting. Gargauth’s spellcasting ability is Charisma (spell save DC 24). Gargauth can innately cast the following spells, requiring no material components. Gargauth can concentrate on two spells at a time that require concentration, but if he loses concentration, he loses both spells.

At will: detect magic, command, fear, produce flame, pyrotechnics, detect thoughts

3/day each: dispel magic, enthrall, fireball, hold monster, insect plague, mislead, obsession (homebrew), revivify, sticks to snakes (homebrew), wall of fire

1/day each: dominate person, eyebite, ice storm, investiture of wind, meteor swarm, teleport

Once every nine days: plane shift

Limited Wish. Gargauth grants a target other than himself a small wish. As an action, he can grant a target one spell that is 6th level or lower and has a casting time of 1 action. The spell can be from any class’s spell list, and the target doesn’t need to meet the requirements in that spell, including costly components; the spell simply takes effect as part of this action. Once Gargauth uses this action, he can’t use it again until he finishes a short rest.

Legendary Resistance (3/Day). If Gargauth fails a saving throw, he can choose to succeed instead.

Magic Resistance. Gargauth has advantage on saving throws against spells and other magical effects, and magic can't put it to sleep.

Magic Weapons. Gargauth’s weapon attacks are magical.

Regeneration. Gargauth regains 20 hit points at the start of his turn, or 10 hit points if he took radiant damage since his last turn. If he takes damage from a weapon that is silvered, this trait doesn’t function at the start of his next turn. Gargauth dies only if he starts his turn with 0 hit points and doesn’t regenerate.

Devil Summoning. By Asmodean decree, Gargauth is unable to summon other devils. However, if a devil sees Gargauth in danger, it will defend The Lord of the Ninth to the best of its abilities, unless its loyalty resides with another pit fiend or archduke. 

Multiattack. Gargauth makes four attacks: three with his fiendish shadow blades (weapons of solidified gloom that appear in his hands) and one with his bite or tail. If in humanoid form, Gargauth can replace the bite or tail attack with his Twisting Words.

Fiendish Shadow Blade. Melee or Ranged Weapon Attack: +16 to hit, reach 10 ft. or range 30/90, one target. Hit: 17 (2d8 + 8) psychic damage plus 21 (6d6) hellfire damage. (Hellfire damage turns fire immunity into fire resistance.) If the target is a flammable object that is not being held or worn, it catches fire. When Gargauth use a shadow blade to attack a target that is in dim light or darkness, he makes the attack roll with advantage.

Bite (true form only). Melee Weapon Attack: +15 to hit, reach 5 ft., one target. Hit: 22 (4d6 + 8) piercing damage. 

Tail (true form only). Melee Weapon Attack: +15 to hit, reach 10 ft., one target. Hit: 24 (3d10 + 8) bludgeoning damage. If the target is a creature, it must succeed on a DC 23 Constitution saving throw or be stunned until the end of its next turn.

Twisting Words. Gargauth targets one creature he can see within 60 feet of him. The target must succeed on a DC 24 Charisma saving throw or take 4d4 psychic damage and be slowed (as per the slow spell) for 1 minute. The target can repeat the saving throw at the end of each of its turns. A creature that succeeds on the saving throw is immune to Gargauth’s Twisting Words for 24 hours.

Invisibility. Gargauth magically turns invisible until he attacks, forces a creature to make a saving throw, or until his concentration ends (as if concentrating on a spell). Any equipment Gargauth wears or carries is invisible with him.

Transmute Metal. Gargauth touches and transforms a metal object that isn't made of silver into gold. 600 gold pieces worth of material can be altered each day. 

Misty Step (Recharge 5-6). Gargauth can misty step. 

Cutting Words (4/day). Gargauth uses his wit to distract, confuse, and otherwise sap the confidence and competence of others. When a creature that he can see within 60 feet of him makes an attack roll, an ability check, or a damage roll, he can use his reaction to roll 1d10 and subtract the number rolled from the creature’s roll. Gargauth can choose to use this feature after the creature makes its roll, but before the DM determines whether the attack roll or ability check succeeds or fails, or before the creature deals its damage. The creature is immune if it can’t hear Gargauth or if it’s immune to being charmed.

Gargauth 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. Gargauth regains spent legendary actions at the start of his turn.

Spell. Gargauth uses Spellcasting.

Confusing Gaze. Gargauth turns his magical gaze toward one creature he can see within 120 feet of him. The target must succeed on a DC 24 Wisdom saving throw or suffer the effect of the confusion spell (no additional saving throw). The effect lasts until the start of Gargauth’s next turn. Gargauth doesn’t need to concentrate on the spell.

Master of Puppets. One creature charmed by Gargauth that Gargauth can see must use its reaction to move up to its speed as Gargauth directs.