Baba Yaga

Crone Sight. Baba Yaga has advantage on Wisdom (Perception) checks that rely on sight. As an action, she can observe a target and magically know its current emotional state. If the target fails a DC 19 Charisma saving throw, she also knows the creature's alignment and discovers a hidden secret about the target.

Crone Speech. Creatures with Intelligence 3 or lower obey Baba Yaga unquestioningly. Her utterances are often captured as engravings on nearby stone and wood surfaces. These magical reproductions of her words are made in the common tongue and fade after several days.

Grandmothers Teeth. The iron teeth of Baba Yaga are sentient, magical, and airborne dentures that sometimes work against the Old Witch. If the teeth and Baba Yaga are getting along, the teeth reside inside her mouth, providing her with a bite attack and access to its spell list. Baba Yaga can cast a spell from the teeth's innate spell list as a bonus action, using her spellcasting ability. Spells cast in this way are removed from the teeth's spell per day total. If the witch and her teeth are not getting along, the teeth will fly around casting spells as it wishes (often to the benefit of Baba Yagas enemies).

Legendary Resistance (5/day). If Baba Yaga fails a saving throw, she can choose to succeed instead.

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

Mortar and Pestle: Baba Yaga flies in a large mortar and pestle, which is immune to damage and can't be the target of spells or effects. It provides the witch partial cover from ranged attacks. Baba Yaga can't provoke an opportunity attack when she flies out of an enemy's reach. If Baba Yaga is knocked prone, stunned, or incapacitated while flying in the mortar, it will gently set her on the ground and disappear for 1 hour. The pestle remains with the witch.  

Spellcasting. Baba Yaga is a 20th-level spellcaster. Her spellcasting ability is Wisdom (spell save DC 21, +14 to hit with spell attacks). Baba Yaga has the following spells prepared:
Cantrips (at will): mage hand, ray of frost, shocking grasp 

1st level (at will): ray of sickness, shield 

2nd level (at will): dragon's breath, wither and bloom

3rd level (at will): animate dead, counterspell

4th level (3 slots): blight, conjure woodland beings, ice storm, phantasmal killer

5th level (3 slots): cloudkill, hold monster, wall of force

6th level (3 slots): chain lightning, circle of death, disintegrate

7th level (3 slots): finger of death, plane shift, teleport

8th level (2 slots): dark star, power word stun, reality break

9th level (2 slots): power word kill, weird

Multiattack. Baba Yaga makes two pestle slap attacks and one bite attack, or three pestle slap attacks.

Bite. Melee Weapon Attack: +10, reach 5 ft., one target. Hit: 37(6d10 + 4) piercing damage and the target must succeed on a DC 20 Wisdom saving throw or become frightened of Baba Yaga until the end of its next turn.

Pestle Slap. Melee Weapon Attack: +10 to hit, reach 10 ft., one target. Hit: 31 (6d8 + 4) blugeoning damage. The target must succeed on a DC 20 Constitution saving throw or have disadvantage in concentration checks until the end of its next turn.

Breath of the Bone Mother.(Recharge 5–6) Ranged Attack: range 40 ft. cone. Calling on her elemental powers and her mastery of crone-magic, Baba Yaga exhales a great wind that smells of fetid mires and sausages. Creatures caught in the area must make a DC 21 Constitution saving throw. On a failure, a target takes 45 (10d8) necrotic damage and is affected by the bestow curse spell for 1 minute. On a success, a target takes half the necrotic damage but is not cursed. 

Countercharm. Baba Yaga throws a powerful charm to disrupt a creature she can see or smell within 60ft in the process of casting a spell. If the creature is casting a spell of 4th level or lower the spell fails and has no effect. If it is casting a spell of 5th level or higher, the creature must succeed on a DC 23 ability check using its spellcasting ability; on a failure, the spell fails and has no effect.

Baba Yaga can take 3 legendary actions, choosing from the options below. Only one legendary action option can be used at the time and only at the end of another creature's turn. She regains spent legendary actions at the start of her turn.

At Will Spell. Baba Yaga casts one at will spell from her list or from her iron teeth's list if equipped.

Breath of the Bone Mother (Costs 2 Actions). Baba Yaga uses Breath of the Bone Mother, if it is available.

Pestle Slap. Baba Yaga makes one pestle slap attack.

Regroup. If she has already used her reaction, Baba Yaga regains the use of her reaction.