Colossal. The dragon is immune to forced movement, does not provoke opportunity attacks and cannot make opportunity attacks. 

In addition, whenever the dragon makes a weapon attack, regardless of whether the attack hits or misses, each creature within 10 feet of the attack's target other than the target or the dragon itself must succeed on a DC 27 Dexterity saving throw or takes half the attack's damage.

Conductive. A creature takes 16 (3d10) lightning damage when it touches the dragon or hits it with a melee weapon attack while within 20 feet of it with a weapon made of metal. If the weapon used for this attack was nonmagical, it is destroyed by lightning.

Empowered Attacks. The dragon's weapon attacks count as magical for the purpose of overcoming resistance and immunity to nonmagical attacks.

Lightning Absorbtion. When the dragon is subjected to lightning damage, it takes no damage and instead regains an amount of hit points equal to the lightning damage.

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

Spellcasting. The dragon is a 20th level spellcaster. It's spellcasting ability is Charisma (spell save DC 23, +15 to hit with spell attacks). It can cast the following spells. requiring no material components:

• Cantrips (at will): gust, lightning lure, mage hand, prestidigitation, thaumaturgy
• 1st level (4 slots): detect magic, identify, earth tremor, shield, thunderwave.
• 2nd level (3 slots): dust devil, Maximilian's earthen grasp, misty step
• 3rd level (3 slots): erupting earth, call lightning, wall of sand
• 4th level (3 slots): death ward, elemental bane, storm sphere
• 5th level (3 slots): summon draconic spirit, legend lore, scrying
• 6th level (2 slots): bones of the earth, primordial ward
• 7th level (2 slots): whirlwind, divine word
• 8th level (1 slot): control weather, earthquake
• 9th level (1 slot): storm of vengeance

Shocking Strikes. When the dragon makes a melee attack against a creature wearing armor made of metal, it has advantage on the attack roll.

Storm Aura. Strong winds blow around the dragon in a 20-feet radius, which extinguish any open flames, impose disadvantage on ranged weapon attacks against it and automatically disperse fog, mists, and similar phenomena in the area, whether mundane or magical.

At the start of the dragon's turn, each creature within that area must succeed on a DC 27 Strength saving throw or take 22 (4d10) bludgeoning damage and be knocked prone.

Treasure Sense. The dragon knows the location of all magic items and of accumulations of mundane treasure within 5 miles of it.

Multiattack. The dragon can use its World-Ending Presence, and if it was flying at the start of its turn, it can use its Crushing Landing. It then makes three attacks: one with its bite and two with its claws.

Bite. Melee Weapon Attack: +19 to hit, reach 25 ft., one target. Hit: 23 (2d12 + 10) piercing damage plus 16 (3d10) lightning damage and the dragon can grapple the target as part of that attack.

Claw. Melee Weapon Attack: +19 to hit, reach 20 ft., one target. Hit: 21 (2d10 + 10) slashing damage plus 16 (3d10) lightning damage. If the target is a creature, it must succeed on a DC 27 strength saving throw or be flung up to 3d4 × 10 feet away from the dragon, landing prone.

Tail. Melee Weapon Attack: +19 to hit, reach 35 ft., one target. Hit: 21 (2d10 + 10) bludgeoning damage plus 16 (3d10) lightning damage and the target must make a DC 27 Strength saving throw or be knocked prone.

World-Ending Presence. Each creature of the dragon's choice that is within 300 feet of the dragon and aware of it must succeed on a DC 23 Wisdom saving throw or drop whatever it was holding and become frightened for 1 minute. A frightened creature must use the dash action on each of its turns, moving as far away from the dragon as it can, using the safest possible route.  If a creature ends its turn in a loaction where it does not have line of sight to the dragon, it can repeat the saving throw, 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 World-Ending Presence for the next 24 hours.

Crushing Landing. If the dragon is flying, it can attempt to land forcefully in a space of its choice, even if that space is occupied by other creatures. When it does so, its movement speed is reduced to 0 until the end of the turn, and each creature in the dragon's space or within 30 feet of it, other than the dragon itself, must make a DC 27 Dexterity saving throw or take 26 (4d12) bludgeoning damage plus 16 (3d10) lightning damage and be knocked prone.

Lightning Breath (Recharge 5–6). The dragon exhales lightning in a 500-foot line that is 20 feet wide. Each creature in that line must make a DC 27 Dexterity saving throw, taking 110 (20d10) lightning damage on a failed save, or half as much damage on a successful one. In addition, on a failed saving throw, a creature is paralyzed until the end of its next turn.

Quicken Spell (3/day). The dragon casts one of its spells of 5th level or lower with a casting time of 1 action.

Lightning Rod. When a creature within 300 feet of the dragon deals lightning damage and the dragon can see that creature, it can use its reaction to draw in the lightning. In this case, the creature targets the dragon with the lightning damage, no matter the effect's original range.

The dragon can take 5 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.

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

Tail Attack. The dragon makes a tail attack.

Wing Attack (Costs 2 Actions). The dragon beats its wings. Each creature within 30 feet of the dragon must succeed on a DC 27 Dexterity saving throw or take 19 (2d8 + 10) bludgeoning damage plus 16 (3d10) lightning damage and be knocked prone. The dragon can then fly up to half its flying speed.

Cast a Spell (Costs 2 Actions). The dragon casts one of its spells of 5th level or lower.

Wind Blast (Costs 3 Actions). The dragon creates a burst of strong wind within 60 feet of it. Each creature within that area must make a DC 27 Strength saving throw. On a failure, it takes 33 (6d10) bludgeoning damage, is hurled up to 3d4 × 10 feet away from the dragon and knocked prone.