Legendary Resistance (4/Day). If Zhengyi fails a saving throw, he can choose to succeed instead.

Undying. If Zhengyi is slain, his soul will return to his Tome, where he will gather energy until he is able to materialize a new body. 

Unusual Nature. Zhengyi doesn’t require air, food, drink, or sleep.

Multiattack. Zhengyi uses Crimson Lightning (if available), Subjugate, or Spellcasting. He then makes two attacks with The Wand of Orcus.

Wand of Orcus. Melee Weapon Attack: +13 to hit, reach 5 ft., one target. Hit: 7 (1d4 + 5) bludgeoning damage plus 9 (2d8) necrotic damage. If the target is a creature, it is afflicted by entropic magic, taking 9 (2d8) necrotic damage at the start of each of its turns.

Crimson Lightning (Recharge 5–6). Zhengyi conjures a torrent of blood red lightning that fills a 120-foot cone and pass through all creatures in that area before dissipating. Each creature in that area must make a DC 22 Constitution saving throw. On a failed save, the creature takes 36 (8d8) lightning damage and is frightened of Zhengyi for 1 minute. On a successful save, the creature takes half as much damage and isn’t frightened. A frightened creature can repeat the saving throw at the end of each of its turns, ending the effect on itself on a success.

Subjugate. Zhengyi causes necrotic magic to engulf one creature he can see within 120 feet of himself. The target must make a DC 22 Constitution saving throw, taking 96 (8d8 + 60) necrotic damage on a failed save, or half as much damage on a successful one. A Humanoid killed by this magic rises as a zombie at the start of Zhengyi’s next turn and acts immediately after Zhengyi in the initiative order. The zombie is under Zhengyi’s control.

Spellcasting. Zhengyi casts one of the following spells, requiring no material components and using Intelligence as the spellcasting ability (spell save DC 22):

At will: animate dead (as an action), detect magic, dispel magic, fly, lightning bolt, mage hand, misty step, prestidigitation

2/day each: chain lightning, dimension door, invisibility, mirror image, scrying (as an action)

1/day each: dominate monster, globe of invulnerability, modify memory, plane shift (self only), power word kill, power word pain

Vile Teleport. Zhengyi teleports, along with any equipment he is wearing or carrying, up to 30 feet to an unoccupied space he can see. He can cause each creature of his choice within 15 feet of his destination space to take 10 (3d6) psychic damage. If at least one creature takes this damage, Zhengyi regains 80 hit points.

Zhengyi can take up to three reactions per round but only one per turn.

Dread Counterspell. Zhengyi utters a dread word to interrupt a creature he can see that is casting a spell. If the spell is 4th level or lower, it fails and has no effect. If the spell is 5th level or higher, Zhengyi makes an Intelligence check (DC 10 + the spell’s level). On a success, the spell fails and has no effect. Whatever the spell’s level, the caster takes 10 (3d6) psychic damage if the spell fails.

Fell Rebuke. In response to being hit by an attack, Zhengyi utters a fell word, dealing 10 (3d6) necrotic damage to the attacker, and Zhengyi teleports, along with any equipment he is wearing or carrying, up to 30 feet to an unoccupied space he can see.

Ultra Focus. As a grandmaster spellcaster, Zhengyi may use up to 2 concentration spells at once. When taking damage, Zhengyi must make 2 separate Con saves.