Archduchess Fierna of Phlegethos

Innate Spellcasting. Fierna's innatte spellcasting ability is Charisma (spell save DC 24, +16 to hit with spell attacks). She can innately cast the following spells, requiring no material components:

At will: charm monster, counterspell, detect magic, dispel magic (5th level), dominate person, fireball, fire bolt (17th level), fire Shield, flame blade (8th level), geas, greater restoration, major image, polymorph, sending, suggestion, teleport, wall of fire

3/day each: dominate monster, fire storm, mass suggestion

1/day each: meteor swarm

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.

Magic Weapons. Fierna's weapon attacks are magical.

Mistress of Flame. Fierna is a master of all spells fire. She is able to add her charima modifier (+9) to one damage roll (once per round) with a spell that deals fire damage. Her spells that deal fire damage also ignore fire resistance. Fierna does not need to maintain concentration on flame blade. 

Regeneration. Fierna regains 10 hit points at the start of her turn. If Fierna 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.

Seductive Aura. Fierna exudes an aura of lust and desire. Any creature that starts its turn with in 30 feet of her must succeed a DC 22 Wisdom saving throw or become charmed by her for 1 minute. While charmed they have disadvantage on saving throws against spells and any other abilities and magical effects caused by Fierna. If the creature takes damage from any source they can make another saving throw. If a creatures saving throw is successful, the creature is immune to Fierna's Seductive Aura for 24 hours.

 Seduction Savant. Fierna has advantage on concentration checks to maintain dominate person and dominate monster.

Multiattack. Fierna attacks twice with her flame blade, or she attacks twice with fire bolt. Fierna can substitute on of her flame blade attacks with a fire bolt.

Flame Blade. Melee Spell Attack: +16 to hit, reach 5 ft., one target. Hit: 30 (6d6 + 9) fire damage. 

Fire Bolt. Ranged Spell Attack: +16 to hit, range 120 ft., one target. Hit: 31 (4d10 + 9) fire damage.

Enthralling Kiss. Fierna kisses a creature charmed by her or a willing creature. The creature must succeed on a DC 22 Wisdom Saving throw or become dominated by her as if under the effects dominate monster. On a success the target takes 36 (5d10 + 9) psychic damage.

Teleport. Fierna magically teleports, along with any equipment she is wearing and carrying, up to 120 ft. 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.

Flame Blade (Costs 1 Actions). Fierna makes one attack with her flame blade.

Fire Bolt (Costs 1 Actions). Fierna Cast fire bolt.

Cast a Spell (Costs 2 Actions). Fierna cast one of her at will spells.

Teleport (Costs 1 Actions). Fierna uses her teleport action.