Boon of Immortality. Tasha is immune to any effect that would age her, and she can’t die from old age.

Planar Guise.  Tasha can choose to appear as a denizen of any of the outer planes including an celestial, fiend or fey. 

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

Magic Resistance. Tasha has advantage on saving throws against spells and other magical effects. (This trait is bestowed by her robe of the archmagi.)

Special Equipment. Tasha wears an amulet of the planes and a robe of the archmagi.

Multiattack.Tasha uses her cauldron if it is available then makes two Bewitching Bolt attacks or casts a spell. 

Bewitching Bolt. Melee or Ranged Spell Attack: +16 to hit, reach 5 ft. or range 120 ft., one target. Hit: 25 (5d6 + 8) lightning damage, and if the target is a creature, it must succeed on a DC 22 Wisdom saving throw or be charmed by Tasha until the start of her next turn.

Tasha's cauldron (Recharge 5–6).  Tasha summons her cauldron at the point within 60ft ft that she can see. A stream of acid sprays from the cauldron in a 30-­foot line that is 5 feet wide in a direction she chooses. Each creature in that line must make a DC 22 Dexterity saving throw, taking 45 (12d8) acid damage on a failed save, or half as much damage on a successful one. A creature that fails it's save is covered in acid for up to one minute or until a creature uses its action to scrape or wash the acid off itself or another creature.

Spellcasting. Tasha casts one of the following spells, requiring no material components and using Intelligence as the spellcasting ability (spell save DC 24, +16 to hit with spell attacks):

At will: detect magic, disguise self, invisibility, light, mage hand, message, prestidigitation, Tasha’s hideous laughter, dispel magic

3/day each:  polymorph, mirror image

1/day each: maze, telekinesis, teleport, wish

Fey Step. Tasha teleports, along with any equipment she is wearing or carrying, to an unoccupied space she can see within 30 feet of her.

Fey Beguilement (1/day). Tasha targets one creature she can see within 60 feet of her that is attacking her or casting a spell. The target must succeed on a DC 22 Charisma saving throw or be possessed by a fey spirit. While possessed, the target must obey Tasha’s commands. The target can repeat the saving throw at the end of each of its turns, banishing the fey spirit and ending the effect on itself on a success.

Tasha 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. Tasha regains spent legendary actions at the start of her turn.

Witchcraft. Tasha uses Spellcasting or Fey Step.