Archduke Dispater of Dis

Ashes to Ashes. Any nonmagical metal that comes into contact with Dispater instantly rusts to ash. This includes any nonmagical weapons used against him.

Divination Defenses. Divination spells of 5th level and lower do not affect Dispater.

Fiery Weapons. Dispater’s weapon attacks are magical. When he hits with any weapon, the weapon deals an extra 36 (8d8) fire damage (included in the weapon attacks below).

Fear Aura. Any creature hostile to Dispater that starts its turn within 20 feet of the archduke must make a DC 26 Wisdom saving throw, unless Dispater 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 Dispater's Fear Aura for the next 24 hours.

Innate Spellcasting. Dispater’s innate spellcasting ability is Charisma (spell save DC 26). He can innately cast the following spells, requiring no material components:

At will: alter self (can become Small when changing his appearance), arcane eye, fireball, invisibility (self only), major image, mislead, scrying, suggestion

3/day each: blade barrier, dominate monster, fear, mass suggestion, project image, steel wind strike

1/day each: forcecage, programmed illusion, teleport

Iron Serpent Strike. The Black Iron Rod of Dis has 10 charges. When Dispater hits with a melee attack using it, he can expend up to 3 of its charges. For each charge expended, the target takes an additional 1d12 force damage.

Legendary Resistance (4/Day). If Dispater fails a saving throw, he can choose to succeed instead.

Magic Resistance. Dispater has advantage on saving throws against spells and other magical effects.

Regeneration. Dispater regains 20 hit points at the start of his turn. If he takes radiant damage, this trait doesn’t function at the start of his next turn. Dispater dies only if he starts his turn with 0 hit points and doesn’t regenerate.

Multiattack. Dispater attacks twice with his rod and once with his Touch of Dis.

Black Iron Rod. Melee Weapon Attack: +16 to hit, reach 5 ft., one target. Hit: 12 (1d6 + 8) bludgeoning damage plus 36 (8d8) fire damage.

Touch of Dis. Dispater touches an object or creature that is within 5 feet of him and bestows one of the following effects:

Dispater attempts to turn a creature's flesh to iron. The creature must succeed on a DC 26 Constitution saving throw or become petrified at the end of its next turn. Constructs are immune to this effect.

Dispater instantly erodes a 10 foot cube of nonmagical metal, leaving nothing but ash. Constructs are immune to this effect. Petrified creatures disintegrated in this way can only be brought back with a true resurrection spell.

Absolute Authority (1/Day). Dispater brandishes his Black Iron Rod for all to see. All creatures within 120 feet of him that he can see must make a DC 15 Wisdom saving throw or become charmed by him for 8 hours. While charmed in this way, the creature regards Dispater as its trusted leader. The charm lasts until the creature is harmed by him or his companions, or commanded to do something contrary to its nature.

Acid Spray (1/Day). Dispater's Black Iron Rod spews acid in a 90-foot line that is 10 feet wide. Each creature in that line must make a DC 22 Dexterity saving throw, taking 63 (14d8) acid damage on a failed save, or half as much on a successful one.

Limited Antimagic Field (1/Day). Dispater's Black Adamantine Armor of Dis conjures a special antimagic field. This antimagic field functions similarly to the traditional spell, except artifacts aren't affected. While this field is up, Dispater cannot cast spells, but his items and other fiendish abilities work fine. Casting antimagic field in this way still requires concentration.

Teleport. Dispater magically teleports, along with any equipment he is wearing or carrying, up to 120 feet to an unoccupied space he can see.

Wall of Iron (3/Day). Dispater conjures a nonmagical wall of iron. This ability functions similarly to the wall of stone spell, except it does not require concentration and the panels have 40 hit points per inch of thickness.

Cruel Puppeteer. When a creature makes an attack roll against Dispater, he can force that creature to roll a DC 26 Wisdom saving throw. On a failed save, the creature instead attacks another creature Dispater can see. On a success, the creature attacks Dispater.

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

Gaze of Dispater (Costs 2 Actions). Dispater turns his magical gaze towards one creature he can see within 120 feet of him, forcing it to relive its worst memory. The creature must make a DC 26 wisdom saving throw. On a success, they take 22 (4d10) psychic damage and shrug off the effect. On a failure, they take this damage and become frightened of Dispater until their next long rest.

Teleport. Dispater uses his Teleport action.

Wall of Iron. Dispater uses his Wall of Iron action.