Elemental Nature. Z'haros does not need to sleep, eat, or breathe. 

Illumination. Z'haros sheds bright light in a 30-foot radius and dim light in an additional 30 feet.

Special Equipment. Z'haros carries a wand of viscid globs and a wand of lightning bolts, and he wears a ring of cinder gift.

Innate Spellcasting. Z'haros' spellcasting ability is Charisma (spell save DC 20). He can innately cast the following spells, requiring no material components:

1/day each: stoneskin, regenerate, true seeing, locate object, Mordenkainen’s Sword, hold person

Multiple Heads. Z'haros has three heads, his draconic head and two heads made of magma. While it has more than one head, he has advantage on saving throws against being blinded, charmed, deafened, frightened, stunned, and knocked unconscious.

Whenever he takes 30 or more damage in a single turn, one of his magma heads dies. If all his magma heads die, he loses this ability until he regains one or more of his magma heads. At the end of his turn, he grows one head for each of its heads that died since its last turn, unless he has taken at least 30 points of cold damage since his last turn. Z'haros regains 25 hit points for each head regrown in this way.

Reactive Heads. For each head Z'haros has beyond one, he gets an extra reaction that can be used only for opportunity attacks.

Limited Water Susceptibility. For every 50 feet Z'haros moves in water, or for every 50 gallons of water splashed on it, it takes 1 cold damage.

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

Multiattack. Z'haros can use his Frightful Presence. he then makes up to five attacks: one bite for each head, two with its claws, and can then create new heads..

Bite. Melee Weapon Attack: +15 to hit, reach 10 ft., one target. Hit: 19 (2d10 + 8) piercing damage plus 7 (2d6) fire damage.

Claw. Melee Weapon Attack: +15 to hit, reach 5 ft., one target. Hit: 15 (2d6 + 8) slashing damage.

Tail. Melee Weapon Attack: +15 to hit, reach 15 ft., one target. Hit: 17 (2d8 + 8) bludgeoning damage.

Frightful Presence. Each creature of the Z'haros' choice that is within 120 feet of him and aware of him must succeed on a DC 20 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 his Frightful Presence for the next 24 hours.

Pyroclastic Breath (Recharge 5–6). Z'haros exhales fire and magma in a 60-foot cone. Each creature in that area must make a DC 22 Dexterity saving throw, taking 63 (18d6) fire damage on a failed save, or half as much damage on a successful one.

If Z'haros has more than 1 head, it can create an eruption of magma and volcanic gas that rapidly cools into stone. Each creature within the breath must make a DC 18 Constitution saving throw. On a failure, the creature takes an additional 2d10 fire damage plus 2d10 poison damage for each magma head not destroyed, and is restrained. It takes half as much damage and is not restrained on a successful one. 

A creature restrained in this way can make a DC 18 Strength saving throw as an action to break out of the cooling magma, ending the effect on itself on a success.

Dual Wand Wielder. If Z'haros is carrying two wands, he can use an action to expend 1 charge from each wand, triggering the effects of both wands simultaneously.

Create Head. Z'haros can create up to two new heads. He loses 25 hit points for each head he creates in this way.

The dragon 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. The dragon regains spent legendary actions at the start of its turn.

Create Head. Z'haros can create up to two new heads. He loses 25 hit points for each head he creates in this way.

Tail Attack. The dragon makes a tail attack.

Wing Attack (Costs 2 Actions). The dragon beats its wings. Each creature within 10 feet of the dragon must succeed on a DC 23 Dexterity saving throw or take 15 (2d6 + 8) bludgeoning damage and be knocked prone. The dragon can then fly up to half its flying speed.