Blighted Mildread, Scourge of the Spring Court

Magical Weapons. Mildread's weapon attacks are considered magical

Creeping Blight. Creatures hit by Mildread's weapon attacks are affected by a creeping blight that slowly spreads up their body. Blighted creatures start by taking 1d4 at the start of their turn, which subsequently increases by 1d4 on every turn afterward, capping out at 5d4. Mildread heals for as much damage as they take.

Nightmarish Presence: Any creature that begins its turn within 30 feet of Mildread must make a DC 18 Wisdom save, or become frightened of Mildread until the end of their next turn. Upon passing the save, a creature is immune to Mildread's Nightmarish Presence for the next 24 hours. 

Legendary Resistences (3/day). When Mildread fails a saving throw, she may choose to succeed instead

Spellcasting. Lady Mildread is an 18th-level spellcaster. Her spellcasting ability is Charisma (spell save DC 18, +12 to hit with spell attacks). Lady Mildread has the following spells prepared:
At will: Ray of Sickness, Inflict Wounds, Cause Fear Toll the Dead
3/day:  Blindness/Deafness, Counterspell, Vitriolic Sphere, Vampiric Touch, Fear
2/day: Bestow Curse, Blight
1/day: Power Word Pain

Multiattack. Blighted Mildread makes two weapon attacks, or one weapon attack and one spell attack.

Blighted Claws. Melee Weapon Attack: +10 to hit, reach 5 ft., 1 target. Hit:  (1d8 + 4) slashing damage. On a hit, the target must make a DC 18 Constitution save or take an additional 3d10 necrotic damage

Lashing Blight. Ranged Weapon Attack: +10 to hit, range 30 ft. Hit: 1d6 + 4 slashing damage. On a hit, the target must make a DC 18 Constitution save, or take 2d10 necrotic damage. Hit targets are pulled to within 5 feet of Mildread, and restrained until she releases them, or until the restrained target spends an action to make a DC 15 Strength check. Mildread may restrain up to two creatures at once with these lashers, and is not able to use them again until they are freed up.

Blighted Rebuke (Recharge 4-6). Upon taking damage, Mildread points a finger at a creature she can see and lets out a ghastly shriek. The target must make a DC 18 Wisdom save. On a failure, the creature takes 3d10 psychic damage, and is frightened of Mildread until the end of their next turn. On a successful save, the creature takes half as much damage and is not frightened. 

Lady Mildread 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. Lady Mildread regains spent legendary actions at the start of her turn.

Attack (Costs 1 Action). Mildread makes a spell attack, or a weapon attack with her claws or lashers.

Blinding Blight (Costs 2 Actions). Mildread points at a blighted creature in range. That creature immediately takes the damage for their current extent of the blight, and must succeed on a DC 18 Constitution save. On a failure, the creature is blinded, and the damage their Blight deals increases to 5d4 for the duration of the blindness. At the start of each of their turns, they may repeat the save, ending the effect on a success. On a success, only the initial damage is taken, and the creature is not blinded. 

Crippling Terror (Costs 3 Actions). Creatures currently frightened must make a DC 18 Wisdom save. On a failure, they take 5d6 necrotic damage, healing Mildread for as much damage dealt. The duration of their fear is then extended for another turn. On a success, the target takes half as much damage, and their fear is not extended.