Lilith

Telepathic Bond. Lilith ignores the range restriction on its telepathy when communicating with a creature she has charmed. The two don't even need to be on the same plane of existence.

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

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

Shapechanger. Lilith can use her action to polymorph into a Small or Medium humanoid, or back into her true form. Without wings, she loses her flying speed. Other than her size and speed, her statistics are the same in each form . Any equipment she is wearing or carrying isn't transformed. She reverts to her true form if she dies.

Spellcasting. Lilith is a 14-level spellcaster. Her spellcasting ability is Charisma (spell save DC 18, +10 to hit with spell attacks). Lilith has following spells prepared:
Cantrips (at will): Friends, Minor Illusion, Vicious Mockery
1st level (4 slots): Puppet, Tasha's Hideous Laughter, Sleep.
2nd level (3 slots): Silence, Phantasmal Force, Zone of Truth
3rd level (3 slots): Dispel Magic, Fear, Hypnotic Pattern, Nondetection
4th level (3 slots): Freedom of Movement, Greater Invisibility, Hallucinatory Terrain
5th level (2 slots): Modify Memory, Dream
6th level (2 slots): Soul Cage
7th level (1 slots): Finger of Death

Lilith can make 2 Claw Attacks or one Tail Attack

Claw (Fiend Form Only). Melee Weapon Attack: +8 to hit, reach 10 ft., one target. Hit: 11 (2d6 + 3) slashing damage.

Tail (Fiend Form Only). Melee Weapon Attack: +8 to hit, reach 10 ft., one target. Hit: 9 (1d10 + 3) slashing damage. The target must make a Constitution Saving Throw or it will take extra 6(1d10) poison damage. 

Charm. One humanoid she can see within 60 feet of her must succeed on a DC17 Wisdom saving throw or be magically charmed. The charmed target obeys her verbal or telepathic commands. At the dawn of each day the target can repeat the saving throw, ending the effect on a success, If the target fails the saving throw for 7 days the charm becomes permanent and can only revert by a wish spell or if Lilith die. Lilith can have as many targets charmed as she likes.

Draining Kiss. Lilith kisses a creature charmed by her or a willing creature. The target must make a DC 17 Constitution saving throw against this magic, taking 53 (8d10 + 5) psychic damage on a failed save, or half as much damage on a successful one. The target's hit point maximum is reduced by an amount equal to the damage taken. This reduction lasts until the target finishes a long rest. The target dies if this effect reduces its hit point maximum to 0.

Not So Fast: When Lilith is targeted with a spell she can make the caster to make a Charisma Saving Throw. On a failed save the caster changer the target to someone hostile to Lilith. 

Lilith has 3 Legendary actions. She can not use the same Legendary action twice in a row.

Charm (Costs 2 Actions). Lilith can use the Charm Action

Invincible (Costs 2 Actions). Lilith can use a 4th level spell slot or higher and cast Greater Invisibility on her. 

Claw (Costs 1 Actions). Lilith can make one claw attacks