Vakratar the eternal storm

Anti magic scales. any magical spells used against Vakratar  instantly fail. Any magical attacks made against him have disadvantage and if they have any modifiers. They are negated if it hits. Spells such as anti magic field can remove this trait temporarily

hatred of magic. If a magical attack or magical spell affects Vakratar. He will go into a rage and target the caster of that spell. While enraged he cannot use his mythic breath weapon. He will stop being enraged when either the caster dies, the caster is out of his line of sight for two rounds. Or he takes 100 or more damage in one hit

chain lightning. when an attack deals lightning damage and only lightning damage. It has a chance to chain to another creature within ten feet of the original target. Dealing has as much damage per chain. (Roll a d4 if an even number. The attack chains. If an odd number the attack does not chain. The dm can either choose to re roll the damage with half the damage dice. Or deal half as much damage equal to the original damage dealt to the original target)

Charged wings. Whenever Vakratar takes off or lands. His wings expel static electricity. Every creature in. 20 feet radius must make a dexterity saving throw of 22 or take 19 (3d8) lightning damage.taking half as much on a successful saving throw. This can only chain on a 2.

chosen by the storm. Whenever Vakratar takes lightning damage. He takes no damage from it and absorbs the damage instead. Up to 100 points of damage. Once he has absorbed 100 points of damage. He can either. Choose to heal himself by 100 points. Or use thunder charge. (If he heals and it goes over his max health. He gains half as much healing as temporary hit points)

thunder charge. Once Vakratar has absorbed 100 points of lightning damage. He can expel it in a 50ft radius. Any creature in that area must make a dexterity saving throw of 23 or take 50 (10d10) lightning damage. Half as much on a successful saving throw. This cannot chain. He must wait until his next turn to use it.

overcharge. If Vakratar takes 20 points or more of lightning damage when he is fully charged for his chosen by the storm ability. He is stunned for one round. He then gains access to his mythic actions

Multi attack. Vakratar makes six attacks. Two with his charged claws. Two with his tail sweep. And two with his charged bite. Or he can use his breath weapon and two charged claws attacks

Charged claws. Melee Weapon Attack: +19 to hit, reach 15 ft., 1 target. Hit: 25 (5d12+ 12) slashing damage. Plus 19 (3d8) lightning damage

Tail Sweep. Melee Weapon attack: +19 to hit, reach 30ft., 3 targets. Hit: 20 (4d12+12) bludgeoning damage

charged bite. melee weapon attack: +19 to hit, reach 10ft., 1 target. Hit. 25 (5d10+12) piercing damage. Plus 19 (3d8) lightning damage. Target is grappled. DC 23. Cannot use breath weapon if a target is grappled

Lightning Breath (Recharge 5–6). Dexterity Saving Throw: DC 24, each creature in a 240-foot-long, 20-foot-wide Line. Failure: 176 (10d20) Lightning damage. Success: Half damage.

Thunder circle. Vakratar breathes a circle of electricity around him. Any creature that moves within five feet of Vakratar and ends its turn there must make a dexterity saving throw of 21 or take 19 (3d8) lightning damage. Taking half as much damage on a successful saving throw. This can only be used if Vakratar has not used his breath weapon.

dive bomb. if Vakratar ends his turn 150 feet in the air. He can dive straight down. Forcing every creature in a 50ft radius to make a dexterity saving throw of 20 or take 19 (3d8) lightning damage. Taking no damage on a successful saving throw.

lightnings vengeance. Whenever Vakratar takes 100 or more damage in one turn. If the creature that dealt that damage is within 5ft of Vakratar at the end of its turn. It must make a dexterity saving throw of 20 or be struck by a stray bolt of lightning from Vakratars skin. Dealing 19 (3d8) lightning. On a faile save and no damage on a successful one

rubble fling. when Vakratar successfully uses dive bomb. As a reaction he can throw some electrically charged rubble at a creature within 30ft of him. The target must make a strength saving throw of 18 or take 19 (3d8) lightning damage. Plus 21 (4d8) bludgeoning damage. If the target scores a natural twenty on this roll they can throw it back at Vakratar. 

Legendary Action Uses: 3 (4 in Lair). Immediately after another creature’s turn, Vakratar can expend a use to take one of the following actions. Vakratar regains all expended uses at the start of each of its turns.

Thunder strike. (Costs 1 action) Vakratar chooses one creature he can see to be struck by a bolt of lightning. (He can also choose himself as a target) the creature takes 23 (4d8) lightning damage. This cannot chain

spark breath. (Costs 1 action) Vakratar clicks his tongue to produce sparks and showers it down on an enemy 15ft front of him. The target must succeed on a dexterity saving throw of 15 or take 12 (2d6+ 3) thunder damage

Lightning combo (costs 3 actions) Vakratar uses his breath weapon attack then if a target is in range uses his tail sweep

Mythic action uses. Vakratar can only use his mythic actions when he has used overcharge. Once he has he regains 200 hit points. Any hit points going over his max health are gained as temporary hit points. Vakratar has 4 mythic actions (5 In his lair) and regains them at the start of his next turn after they are all spent. His breath weapon is also replaced by the following mythic action. 

Vessel of storm. Maximum blast (Costs 1 Action). Vakratar charges up a beam of lightning in his throat. Gaining an obvious glow and allowing creatures to use a reaction to run in any direction. He then fires a beam of lightning for 400ft in a 40ft wide line. Dealing 452 (20d20+100) lightning damage. Optionally he can fire this whilst in the air (maximum 50ft) allowing him to move the beam 20 feet in any directions whilst airborne. he can expend 2 mythic actions to carry on the blast for another turn. any creature caught in the blast must make a dexterity saving throw of 24 or become stunned for one turn. Once that turn has ended they are blasted away 50 ft  from the blast. And are knocked prone. Vakratar can use his thunder strike on every creature caught in the blast. Without using a legendary action.

Storms Call. (3 actions)   Vakratar roars. Expelling all his electricity gained from chosen by the storm. Creating a storm for 100 feet. Any creature in this area must make a dexterity saving throw of 20 or be hit by a lightning bolt. Taking 19 (3d8) lightning damage. Vakratars flying speed is also increased to 150 feet. At the end of his turn. He is hit by a lightning bolt as well as everyone else within the radius of the storm. Lightning damage also increases. Dealing an extra 1d12 of damage. 

pride of the storms chosen.(2 actions)  Vakratar sends an electric wave of energy for 120 feet from his wings  each creature must make a dexterity saving throw of 21 or be stunned for 2 turns. not being stunned if they succeed the saving throw. any creature caught in this and fails the saving throw takes double damage from vessel of storm maximum blast.  

Last cry. (All mythic actions) When Vakratar drops to zero hit points. He regenerates one hit point. And his AC increases by 5. His lair starts to collapse. All creatures at the end of their turn must make a strength  saving throw of 20 or be pinned down by rubble. Taking 1d4 damage for Ee very other creatures  turn it has been pinned. A successful strength saving throw of 20 will allow them to shrug off the rubble. Vakratar must also make this saving throw but can choose to succeed it up to 4 times. On the fifth being completely buried and dying.