Archduchess Fierna of Phlegethos

Devil’s Sight. Magical darkness doesn’t impede Fierna’s darkvision.

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

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

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

Multiattack. Fierna uses Hurl Meteor (if available) or Spellcasting. She then makes two attacks with her scimitar.

Scimitar. Melee Weapon Attack: +18 to hit, reach 10 ft., one target. Hit: 17 (2d8 + 8) radiant damage plus 36 (8d8) fire damage.

Hurl Meteor (Recharge 5–6). Fierna conjures a blazing orb that strikes the ground, exploding in an area up to 120 feet away from her that she can see. Each creature within the 20-foot-radius sphere explosion must make a DC 26 Dexterity saving throw, taking 28 (8d6) force damage and 28 (8d6) fire damage on a failed save, or half as much damage on a successful one.

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

At will: alter self (can become Medium when changing her appearance), detect evil and good, dispel magic, fireball, invisibility (self only), wall of fire

3/day each: fire storm, dispel evil and good, finger of death

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

Fierna 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. Fierna regains spent legendary actions at the start of her turn.

Tempting Gaze (Costs 2 Actions). Fierna turns her magical gaze toward one creature she can see within 120 feet of her and violently drains its willpower. The target must succeed on a DC 26 Wisdom saving throw or take 22 (4d10) psychic damage and be charmed by Fierna until the start of her next turn.

Teleport. Fierna uses Teleport.