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

Bloody Rage. When Z'gorath is brought below half of his maximum hit points (below 300) he is enraged, while in this state (within the hit point threshold) his breath weapon recharges on a 4-6, he gains an additional legendary action per round, and he gains the Rend legendary action option. 

Orb of Dragonkind. Z'gorath possess a powerful artifact that grants him a few abilities. The Orb can be utilized once per day to gain control over a lesser dragon for a number of days equal to the difference in challenge rating between the two dragons. Additionally, the Orb has 20 charges that can be used to cast a number of spells listed below, the orb regains 2d8 +4 expended charges daily at dawn. 

• Spells. While holding the orb Z'gorath can use an action to expend 1 or more of its charges to cast one of the following spells from it, using your spell save DC and spell attack bonus (+13 to hit, spell DC 21). : scrying (3 charges), fireball (2 charges), hold monster (3 charges), dispel magic (2 charges), cure wounds (5th-level version, 3 charges), ray of enfeeblement (1 charge), or wall of fire (2 charges).  

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: +17 to hit, reach 15 ft., one target. Hit: 21 (2d10 + 10) piercing damage plus 14 (4d6) fire damage.

Claw. Melee Weapon Attack: +17 to hit, reach 10 ft., one target. Hit: 17 (2d6 + 10) slashing damage.

Tail. Melee Weapon Attack: +17 to hit, reach 20 ft., one target. Hit: 19 (2d8 + 10) bludgeoning damage.

Frightful Presence. Each creature of the dragon's choice that is within 120 feet of the dragon and aware of it must succeed on a DC 21 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 the dragon's Frightful Presence for the next 24 hours.

Fire Breath (Recharge 5–6). The dragon exhales fire in a 90-foot cone. Each creature in that area must make a DC 24 Dexterity saving throw, taking 91 (26d6) fire damage on a failed save, or half as much damage on a successful one.

The dragon can take 3 legendary actions (4 while in a bloody rage), 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. The dragon regains spent legendary actions at the start of its turn.

Cast a spell (costs 2-3 Actions). The dragon uses some of the Orb's charges to cast a spell from its list, if the spell is 3rd level or lower it costs 2 legendary actions, otherwise it costs 3.

Tail Attack. The dragon makes a tail attack.

Wing Attack (Costs 2 Actions). The dragon beats its wings. Each creature within 15 feet of the dragon must succeed on a DC 25 Dexterity saving throw or take 17 (2d6 + 10) bludgeoning damage and be knocked prone. The dragon can then fly up to half its flying speed.

Rend (Requires Bloody Rage, Costs 2 Actions). The dragon makes 2 claw attacks simultaneously, if both attacks hit the target they must make a DC 25 Strength save or be thrown 30 feet directly away from Z'gorath, if the attack causes the target to collide with a surface they suffer 1d6 fall damage for every 10 feet thrown, landing prone on the surface.