Arzzargorn the Annihilator (Pit Fiend)

Fear Aura. Any creature hostile to the pit fiend that starts its turn within 30 feet of the pit fiend must make a DC 22 Wisdom saving throw, unless the pit fiend is incapacitated. On a failed save, the creature is frightened until the start of its next turn. If a creature's saving throw is successful, the creature is immune to the pit fiend's Fear Aura for the next 24 hours.

Innate Spellcasting. The pit fiend's spellcasting ability is Charisma (spell save DC 22). The pit fiend can innately cast the following spells, requiring no material components:

At will: Control Flames, Darkness, Detect Magic, Fireball, Minor Illusion

3/day each: Hold Monster, Programmed Illusion, Wall of Fire

2/day each: Divine Word, Power Word Stun

1/day each: Meteor Swarm

Magic Resistance. The pit fiend has advantage on saving throws against spells and other magical effects.

Magic Weapons. The pit fiend's weapon attacks are magical.

Multiattack. The pit fiend makes four attacks: one with its bite, one with its claw, one with its trident, and one with its tail.

Bite. Melee Weapon Attack: +16 to hit, reach 5 ft., one target. Hit: 23 (4d6 + 9) piercing damage. The target must succeed on a DC 23 Constitution saving throw or become poisoned. While poisoned in this way, the target can't regain hit points, and it takes 21 (6d6) poison damage at the start of each of its turns. The poisoned target can repeat the saving throw at the end of each of its turns, ending the effect on itself on a success.

Claw. Melee Weapon Attack: +16 to hit, reach 10 ft., one target. Hit: 18 (2d8 + 9) slashing damage. On a hit, if the target is Medium or smaller, it is grappled (escape DC 19). Until this grapple ends, the target is restrained and the pit fiend can automatically hit the target with its claw but can't make claw attacks against other targets.

Trident. Melee Weapon Attack: +16 to hit, reach 15 ft., or range 40/100 ft., one target. Hit: 18 (2d8 + 9) piercing damage plus 36 (8d8) fire damage. If thrown, the pit fiend can use a bonus action to have the trident magical teleport to its open hand.

Tail. Melee or Ranged Weapon Attack: +16 to hit, reach 10 ft., one target. Hit: 25 (3d10 + 9) bludgeoning damage. On a hit, the target must make a DC 19 Strength saving throw or fall prone.

Summon Devil (1/Day). The devil chooses what to summon and attempts a magical summoning.

A pit fiend summons 3d4 Bearded Devil, 2d4 Barbed Devil, or 1d4 Erinyes with no chance of failure.

A summoned devil appears in an unoccupied space within 60 feet of its summoner, acts as an ally of its summoner, and can’t summon other devils. It remains for 1 minute, until it or its summoner dies, or until its summoner dismisses it as an action.

Teleport. The pit fiend magically teleports, along with any equipment it is wearing or carrying, up to 60 feet to an unoccupied space it can see.

The pit fiend 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. The pit fiend regains spent legendary actions at the start of its turn.

Attack. The pit fiend attacks once with its claw or tail.

Cast a Spell (Costs 2 Actions). The pit fiend casts a spell from its list of innate spells, using a spell slot as normal.

Teleport (Costs 2 Actions). The pit fiend magically teleports, along with any equipment it is wearing or carrying, up to 60 feet to an unoccupied space it can see.