Advocatus, Dealer in Souls

Diabolical Restoration. If Advocatus dies outside the Nine Hells, his body disappears in sulfurous smoke, and he gains a new body instantly, reviving with all of his Hit Points in his lair in the Nine Hells.

Magic Resistance. Advocatus has Advantage on saving throws against spells and other magical effects while in his lair.

Legendary Resistance (2/Day, or 5/Day in Lair). If Advocatus fails a saving throw, he can choose to succeed instead.

Multiattack. Advocatus makes three attacks, using Searing Blade. It can replace one attack with a use of Infernal Dirk.

Searing Blade. Melee Attack Roll: +10, reach 10 ft. Hit: 14 (3d6 + 4) Slashing damage. On a roll of 6 on any of the attack dice, add an additional 3 (d6) Fire Damage.

Infernal Dirk. Melee or Ranged Attack Roll: , +12 ], reach 5 ft. or range 60 ft. Hit: 9 (2d4 + 4) Piercing damage. Additionally, the target must make a DC 15 Constitution Check. Failure: The target receives an infernal wound if it doesn’t have one. While wounded, the target 3 (d6) Fire damage at the start of each of its turns. The wound closes after 1 minute, after a spell restores Hit Points to the target, or after the target or a creature within 5 feet of it takes an action to stanch the wound, doing so by succeeding on a DC 15 Wisdom (Medicine) check. If Advocatus and the target are both in his lair, both DCs are increased to DC 17, and the wound deals 10 (3d6) Fire damage at the start of each of its turns and heal Advocatus the same amount, instead.

Spellcasting. Advocatus casts one of the following spells, using Charisma as the spellcasting ability (spell save DC 16):

At Will: Detect Magic, Detect Thoughts, Prestidigitation, Scrying
2/Day Each:Invisibility, Dispel Magic, Fireball (level 3 version), Plane Shift (only on self)

Summon Barbed Devil. Once a day, Advocatus may summon a [creatures]barbed devil[/creatures] at any point he can see within 50 ft. The creature follows his orders until it is dismissed by him. If Advocatus is in his lair, he may summon the creature at any location inside of his lair, and has unlimited uses per day, though only one per turn. 

Burning Counterspell. Advocatus casts Counterspell in response to the spell’s trigger, using the same spellcasting ability as Spellcasting. The caster of the countered spell takes 3 (d6) Fire damage.  If Advocatus is in his lair, the target then takes 7 (2d6) Fire damage instead.

Legendary Action Uses: 2 (5 in Lair). Immediately after another creature’s turn, Advocatus can expend a use to take one of the following actions. Advocatus regains all expended uses at the start of each of his turns.

Infernal Barbs. Advocatus casts Silvery Barbs in response to another creature succeeding an attack roll, an ability check, or a saving throw. If Advocatus is in his lair, the target then takes 7 (2d6) Fire damage.

Summon Imp. Advocatus may summon a [creatures]imp[/creatures] at any point he can see within 50 ft. of him. Advocatus may then not use this ability until the start of his next turn. The creature follows his orders until it is dismissed by him. If Advocatus is in his lair, he may summon the creature at any location inside of his lair.

Burning Teleport. Advocatus teleports up to 60 feet to an unoccupied space it can see, and each creature within 10 feet of the space he left takes 7 (2d6) Fire damage. If Advocatus is in his lair, the target takes 14  (4d6) Fire damage instead

Burning Strike. Advocatus moves up to half his movement speed and makes one Searing Blade attack.

(2 Actions) Infernal Whisper. Advocatus targets one creature it can see within 120 feet of itself. The target must succeed on a DC 14 Wisdom saving throw or take 11 (2d6 + 4) psychic damage and get a -1 on all rolls (to a minimum of 1) until the end of Advocatus' next turn as incomprehensible whispers fill the target’s mind. If Advocatus is in his lair, the DC rises to 17, the damage is increased to 18 (4d6 + 4) psychic damage and the target is stunned instead.

(3 Actions) Summon Horned Devil. If Advocatus is in his lair, he summons a [creatures]horned devil[/creatures] at any point he can see within 50 ft. of him. The creature follows his orders until it is dismissed by him. Advocatus may only use this ability once every hour.