Cloaked in Shadow (3/day). If Zehir is hit with an attack while in dim light or darkness, he may force the attaacker to reroll the attack. They must use the new result.

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

Lord of Shadow. Double the range and triple the size of any darkness spell cast by Zehir. Additionally, darkness cast by Zehir is considered a 3rd level spell, and cannot be pierced or dispelled by magical light of the same level or lower. Zehir can have 1 instance of darkness active without concentration, as long as it is anchored to an item on him.

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

Strike from the Shadows. When Zehir hits with an attack while in dim light or darkness, the target takes an additional 11 (2d10) poison damage. 

The Origin Poison. Poison damage dealt by Zehir cannot be reduced by Poison Resistance. Additionally, Poison Immunity only halves the damage.

Multiattack. Zehir makes 2 Claw attacks, 1 Constrict attack or At Will Spellcasting, and 1 Bite or Poison Spit attack. Alternatively, Zehir can make one Frightful Presence and one Spellcasting attack.

Bite. Melee Weapon Attack: +13 to hit, reach 10 ft., one target. Hit: 15 (2d8+6) piercing damage plus 18 (4d8) poison damage. The target must succeed on a DC 24 Constitution saving throw or be poisoned. While poisoned in this way, the target takes 11(2d10) poison damage at the start of their turn. The target can repeat the saving throw at the end of each of its turns, ending the effect on itself on a success.

Claw. Melee Weapon Attack: +13 to hit, reach 10 ft., one target. Hit: 22 (3d10+6) slashing damage plus 9 (2d8) poison damage

Constrict. Ranged Spell Attack: range 60 ft., one target. Zehir conjures ethereal snakes around a target within range. The target must succeed on a DC 24 Dexterity saving throw or take 13 (3d8) bludgeoning damage and be grappled (escapde DC 24). While grappled the target is also restrained and takes 13 (3d8) poison damage at the start of their turn.

Frightful Presence. Each creature of Zehir's choice that is within 120 feet of him and aware of him must succeed on a DC 24 Wisdom saving throw or become frightened for 1 minute. A creature can repeat the saving throw at the end of each of its turns, ending the effect on itself on a success. If a creature’s saving throw is successful or the effect ends for it, the creature is immune to Zehir’s Frightful Presence for the next 24 hours.

Poison Spit. Ranged Weapon Attack: +13 to hit, range 60/240 ft., one target. Hit: 22 (4d10+9) poison damage. The target must succeed on a DC 24 Constitution saving throw or be poisoned. While poisoned in this way, the target takes 11(2d10) poison damage at the start of their turn. The target can repeat the saving throw at the end of each of its turns, ending the effect on itself on a success.

Spellcasting. Zehir casts one of the following spells, requiring no material components and using Charisma as the spellcasting ability (spell save DC 24):

At Will: detect poison and disease, mage hand, poison spray (17th level), ray of sickness (3rd level), suggestion

3/Day each: cloudkill, shadow of moil, vitriolic sphere

1/Day each: dark star, dominate monster, forcecage, maddening darkness

Poisonous Shadow Vault. Zehir can teleport up 60 ft provided both the starting and ending points are in dim light or darkness. Any creature within 15 ft of Zehir after the teleport must succeed on a DC 24 Constitution saving throw or take 13 (2d12) poison damage. If there are no cretures within 15 ft of Zehir after the teleport, he may instead regain 26 (4d12) hit points.

Zehir 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. Zehir regains spent legendary actions at the start of his turn.

Grasping Coils. Zehir uses his Constrict attack.

Greater Spellcasting (Costs 2 Actions). Zehir casts one of his 3/day spells.

Father of the Yuan-Ti (Costs 3 actions). Zehir summons Yuan-Ti reinforcements fanatically loyal to him. Roll a d100 and refer below.

• 01-20 4 Yuan-Ti Purebloods and 3 Giant Constrictor Snakes are summoned
• 21-40 3 Yuan-Ti Malisons (type determined by a d3) and 4 flying snakes are summoned
• 41-60 2 Yuan-Ti Poison Fangs and 4 Yuan-ti Broodguards are summoned
• 61-80 2 Yuan-Ti Abominations are summoned  
• 81-00 1 Yuan-Ti Anathema is summoned