Legendary Resistance (3/Day). If the dragon fails a saving throw, it can choose to succeed instead.

Light Eater. A creature reduced to 0 hit points from damage dealt by Zaryn dies and can’t be revived by any means short of a wish  spell.

Miasma.  Any creature that starts its turn within 30 feet of Zaryn must succeed on a DC 21 Constitution saving throw or take 24 (6d6) necrotic damage and grant Zaryn advantage on attack rolls against it until the start of the creature’s next turn. Undead are immune to this effect. 

Shapeshift. Zaryn can choose to appear almost completely human, losing all but his claw attacks. 

Legendary Vulnerability. For every 10 points of Lightning damage taken, reduce AC by 1.

Multiattack. The dragon can use its Frightful Presence. It then makes three attacks: one with its bite and two with its claws.

Bite. Melee Weapon Attack: +18 to hit, reach 15 ft., one target. Hit: 30 (3d10 + 10) piercing damage plus 12 (3d8) acid damage.

Claw. Melee Weapon Attack: +18 to hit, reach 10 ft., one target. Hit: 20 (3d6 + 10) slashing damage.

Tail. Melee Weapon Attack: +15 to hit, reach 20 ft., one target. Hit: 22 (3d8 + 10) bludgeoning damage.

Frightful Presence. Each creature of Zaryn's choice that is within 120 feet of the dragon and aware of it must succeed on a DC 19 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 Zaryn's Frightful Presence for the next 24 hours.

Acid Breath (Recharge 5–6). Zaryn exhales acid in a 60-foot line that is 30 feet wide. Each creature in that line must make a DC 22 Dexterity saving throw, taking 32  (8d8) acid damage on a failed save, or half as much damage on a successful one.

Poison Breath (Recharge 5-6). .Zaryn inhales deeply and exhales a poisonous cloud in a 60-foot cone. Each creature in the cone must make a DC 22 Dexterity saving throw, taking 32 (8d8) poison damage on a failed save, or half as much damage on a successful one. 

Deaths Touch (Recharge 3-4). Once per turn, Zaryn can make a grapple on a creature within 10 feet. The creature must make a DC 22 Athletics or Acrobatics saving throw. If the creature fails, it takes 50 (10d10) necrotic damage and must make additional throws to escape its grasp, taking 18 (6d6) necrotic damage on each failed saving throw. 

Zaryn 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. Zaryn regains spent legendary actions at the start of its turn.

Detect. The dragon makes a Wisdom (Perception) check.

Bite Attack. The dragon makes a bite attack.

Wing Attack (Costs 2 Actions). Zaryn beats his wings. Each creature within 15 feet of the dragon must succeed on a DC 23 Dexterity saving throw or take 15 (2d6 + 8) bludgeoning damage and be knocked prone. Zaryn can then fly up to half his flying speed.

Raise Dead (Costs 3 Actions). Zaryn slams his claw into the ground, causing a huge shockwave. Each creature within 30 feet must succeed on a DC 23 Dexterity saving throw or take 25 (3d6+8) damage and be knocked prone. He then raises 1d8 Undead Thrall who fight for him for 1 minute or until killed. Can only be used once per minute.