Legendary Resistance (6/day). If Tharizdun fails a saving throw, he can choose to succeed instead.

Antimagic Cone. Tharizdun can create an area of antimagic, as in the antimagic field spell, in a 150-foot cone. At the start of Tharizdun's turn, he can choose which way the cone faces. Tharizdun can dismiss the cone or activate it as a bonus action. The cone doesn't function if Tharizdun is incapacitated.

Disincorporation. When Tharizdun drops to 0 hit points, his avatar form is destroyed, but his essence travels back to his prison just beyond the Multiverse. He is unable to take physical form for an unknown amount of time.

Limited Magic Immunity. Tharizdun is immune to spells of 5th level or lower unless he wishes to be affected. He also has advantage on saving throws against spells and spell-like effects.

Shapechange. Tharizdun can transform himself and any equipment he has into a form resembling any sentient creature of a small or larger size. Tharizdun can choose the make this form look however he wants, but all of his statistics remain the same in this new form. A creature can determine that the creature is Tharizdun by succeeding on a DC 27 Wisdom (Insight) or Wisdom (Religion) check.

Incorporeal Form (3/day). Tharizdun can, as a bonus action, turn himself incorporeal. While in this form, Tharizdun can move through solid objects and creatures as if they were difficult terrain and all attacks against Tharizdun have disadvantage. This effect lasts until the start of his next turn and if Tharizdun ends his turn inside of another object's space, he takes 55 (10d10) force damage that ignores damage resistance. and is immediately shunted into the nearest unoccupied space. While in this form he is immune to the grappled and restrained conditions for the duration.

Regeneration. Tharizdun regains 30 hit points at the start of his turn unless he is incapacitated or takes damage from a good-aligned creature.

Eldritch Weapons. Tharizdun's weapon attacks are magical, also when Tharizdun hits a creature with a weapon attack the creature that was hit takes an additional 38 (6d10) psychic damage (this damage is included in the attack).

Essence of Eldritch Magic. Tharizdun can concentrate on up to 3 spells at a time. If he casts another concentration spell while concentrating on 3 other spells, he can choose one spell he was concentrating on and end its effects immediately.

Innate Spellcasting. Tharizdun's spellcasting ability is Charisma (save DC 27, +19 to hit with spell attacks). Tharizdun can cast the following spells innately, requiring no spell components.

At will: shape water, mold earth, control flames, gust, toll the dead, eldritch blast (6 bolts, +10 to damage rolls), hold monster, lightning bolt, banishment, polymorph, fireball

3/day: divine word, disintegrate, plane shift, fire storm, chain lightning, prismatic spray, harm, geas, soul cage

1/day: feeblemind, reverse gravity, meteor swarm, power word kill, time stop