Valaine

Innate Spellcasting. Valaine's spellcasting ability is Charisma (spell save DC 22, +15 to hit with spell attacks). She can innately cast the following spells, requiring no material components:
At will: chill touch (17th level), Darkness, detect magic, dispel magic.
1/day each: time stop, power word kill, wish, mind blank, invulnerability.

Always Home. Valaine always considered to be on her home plane for the purpose of banishing spells.

Beyond Life. Valaine does not require food, water, sleep, and she can breathe in any conditions.

Undetectable. Valaine can't be targeted by divination magic, perceived through magical scrying sensors, or detected by abilities the sense demons or fiends.

Devil's Sight. Valaine can see through darkness, magical and non-magical, to a range of 120 ft.

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

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

Magic Weapons. Valaine's weapon attacks are magical.

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

Fiendish Mind. Any creature that isn't a Fiend that starts its turn within 30 feet of Valaine must succeed on a DC 18 Wisdom saving throw, or it hears a faint buzzing in its head for a moment and is subject to the confusion spell for 18 seconds (3 rounds) with no concentration required by Valaine. If the creature succeeds the saving throw they are immune to Fiendish Mind for one day. 

Violate Corpse. Valaine can use a bonus action to possess a corpse to make it do something unnatural, such as vomit blood, twist its head all the way around, or cause a quadruped to move as a biped. Any beast or humanoid that sees this behavior must succeed on a DC 12 Wisdom saving throw or become frightened for 1 minute. The frightened creature can repeat the saving throw at the end of each of its turns, ending the effect on itself on a success. A creature that succeeds on a saving throw against this ability is immune to Violate Corpse for 24 hours.

Devour Soul. Valaine can eat the soul of a creature she has killed within the last hour, provided that creature is neither a construct nor an undead. The devouring requires Valaine to be within 5 feet of the corpse for at least 10 minutes, after which it gains a number of Hit Dice (d20s) equal to half the creature’s number of Hit Dice. Roll those dice, and increase Valaine's hit points by the numbers rolled. A creature devoured by a nabassu can be restored to life only by a wish spell.

Multiattack. Valaine must use her Frightful Presence and then she makes four attacks: two with her claws, one with her tail, and one with her Demonic Weapon.

Claws. Melee Weapon Attack: +17 to hit, reach 5 ft., one target. Hit: 18 (2d10 + 8) slashing damage plus 8 (2d8) poison damage. 

Tail. Melee Weapon Attack: +17 to hit, reach 20 ft., three targets. Hit: 26 (4d8 + 8) piercing damage damage plus 12 (3d8) bludgeoning damage. 

Demonic Weapon. Melee Weapon Attack: +17 to hit, reach 10 ft., one target. Hit: 37 (6d8 + 9) slashing damage. If the target has at least one head and Valaine rolled a 20 on the attack roll, the target is decapitated and dies if it can’t survive without that head. A target is immune to this effect if it takes none of the damage, has legendary actions, or is Huge or larger. Such a creature takes an extra 8d8 slashing damage from the hit.

Frightful Presence. Each creature of Baphomet’s choice within 120 feet of him and aware of him must succeed on a DC 18 Wisdom saving throw or become frightened for 1 minute. A frightened creature can repeat the saving throw at the end of each of its turns, ending the effect on itself on a success. These later saves have disadvantage if Baphomet is within line of sight of the creature. If a creature succeeds on any of these saves or the effect ends on it, the creature is immune to Baphomet’s Frightful Presence for the next 24 hours.

Roar of Hell. Valaine emits a frightening roar that can affect creatures up to 90 feet away. Each creature within 90 feet of Valaine that is not a fiend must make a DC 19 Dexterity saving throw, taking 66 (12d10) fire damage on a failed save or half as much on a successful one. Additionally, creatures in the area must make a DC 21 Constitution saving throw, taking 33 (6d10) psychic damage and becoming deafened for 1 minute on a failed save or half as much damage and are not deafened on a successful one. 

Summon Demon. Enter the description for your action.

Gaze. Demogorgon turns his magical gaze toward one creature that he can see within 120 feet of him. That target must make a DC 23 Wisdom saving throw. Unless the target is incapacitated, it can avert its eyes to avoid the gaze and to automatically succeed on the save. If the target does so, it can’t see Demogorgon until the start of his next turn. If the target looks at him in the meantime, it must immediately make the save. If the target fails the save, the target suffers one of the following effects of Demogorgon’s choice or at random:

1. Beguiling Gaze. The target is stunned until the start of Demogorgon’s next turn or until Demogorgon is no longer within line of sight.
2. Hypnotic Gaze. The target is charmed by Demogorgon until the start of Demogorgon’s next turn. Demogorgon chooses how the charmed target uses its actions, reactions, and movement. Because this gaze requires Demogorgon to focus both heads on the target, he can’t use his Maddening Gaze legendary action until the start of his next turn.
3. Insanity Gaze. The target suffers the effect of the confusion spell without making a saving throw. The effect lasts until the start of Demogorgon’s next turn. Demogorgon doesn’t need to concentrate on the spell.

Reaction Name. Enter the description for your action.

Valaine can take 4 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. Valaine regains spent legendary actions at the start of her turn.

Cast a Spell. Valaine can cast a spell using her Innate Spellcasting trait.

Lord of Hell (Costs 2 Actions). Valaine can use her Gaze, Summon Demon, or Roar of Hell action.  

Devils' Wings (Costs 2 Actions). Valaine beats her wings. Each creature within 30 feet of her must make a DC 20 strength saving throw or take 20 (4d6 + 7) bludgeoning damage and be pushed 10 feet away from Valaine, being knocked prone in the process. On a successful save, targets take no damage and are not moved away but are knocked prone. Valaine can then move up to half her flying speed.