Archduke Zariel of Avernus (2024 Version)

Diabolical Restoration. If Zariel dies outside the Nine Hells, her body disappears in sulfurous smoke, and she gains a new body instantly, reviving with all her Hit Points somewhere in Avernus.

Legendary Resistance (4/Day, or 5/Day in Lair). If Zariel fails a saving throw, she can choose to succeed instead.

Magic Resistance. Zariel has Advantage on saving throws against spells and other magical effects.

Regeneration. Zariel regains 30 Hit Points at the start of each of her turns. If Zariel takes Radiant damage, this trait doesn't function on Zariel's next turn. Zariel dies only if she starts her turn with 0 Hit Points and doesn't regenerate.

Multiattack. Zariel makes three Flail attacks. She can replace one attack with a use of (A) Horrid Touch (if available), (B) Matalotok, or (C) Teleport.

Flail. Melee Attack Roll: +16 to hit, reach 10 ft. Hit: 17 (2d8 + 8) Force damage plus 36 (8d8) Fire damage. Zariel also creates one of the following effects:

Focus. Zariel adds 1d8 to the next attack roll she makes before the end of her next turn.

Maneuver. One ally who can see or hear Zariel can take a Reaction to move up to half the ally's Speed without provoking Opportunity Attacks.

Sap. The target has Disadvantage on its next attack roll before the start of Zariel's next turn.

Matalotok. Melee Attack Roll: +16 to hit, reach 10 ft. Hit: 17 (2d8 + 8) Bludgeoning damage plus 36 (8d8) Fire damage, and each creature in a 30-foot Emanation originating from Zariel takes 10 (3d6) Cold damage.

Horrid Touch (Recharge 5–6). Constitution Saving Throw: DC 26, one creature Zariel can see within 10 feet. Failure: 78 (12d12) Necrotic damage, and the target has the Poisoned condition for 1 minute. While Poisoned, the target has the Blinded and Deafened conditions. Success: Half damage only.

Spellcasting. Zariel casts one of the following spells, requiring no Material components and using Charisma as the spellcasting ability (spell save DC 26):

At Will: Detect Evil and Good, Fireball (level 9 version), Invisibility, Major Image, Shapechange (Beast or Humanoid form only, no Temporary Hit Points gained from the spell, and no Concentration or Temporary Hit Points required to maintain the spell), Wall of Fire (level 9 version)

3/Day Each: Blade Barrier, Dispel evil and Good, Finger of Death

Teleport. Zariel teleports up to 120 feet to an unoccupied space she can see.

Legendary Action Uses: 3 (4 in lair). Immediately after another creature's turn, Zariel can expend a use to take one of the following actions. Zariel regains all expended uses at the start of each of her turns.

Blazing Teleport. Zariel uses Teleport. Dexterity Saving Throw: DC 26, each creature in a 20-foot Emanation originating from Zariel at her destination space. Failure: 16 (3d10) Fire damage. Success: Half damage. 

Dread Authority. Zariel casts Command (level 3 version), using the same spellcasting ability as Spellcasting. Zariel can't take this action again until the start of her next turn.

Immolating Gaze. Charisma Saving Throw: DC 26, one creature Zariel can see within 120 feet. Failure: 33 (6d10) Fire damage, and the target starts burning, taking 5 (1d10) Fire damage at the start of each of its turns instead of the normal burning damage. The target gains 1 Exhaustion level whenever it takes this burning damage. Success: Half damage only. Failure or Success: Zariel can't take this action again until the start of her next turn.