Ancient Verdant Fog-Born Dragon

High Fliers. The dragon can breathe in any area that has an amount of air, no matter how thin. It can hold its breath for up to an hour at a time.

Verdant Scales. The dragon's flight speed is doubled while in clean air. If the dragon moves at least 120 feet in a straight line before attacking, the attack deals an additional 28 (8d6) damage. Effects, climates, or conditions which pollute or exist instead of air; including but not limited to volcanic eruptions, the Fog Cloud spell, the smoke of a forest fire, and the dragon being underwater are considered to not be clean air for the purposes of this trait.

Fade Into Fog. The dragon can use its action to shapechange into a mass of semisolid air (or back to its dragon form). While in this form, the dragon makes stealth checks at advantage and loses its walking and swimming speeds, but gains the hover property.

Spellcasting. The dragon is an innate spellcaster. Its spellcasting ability is charisma (spell save DC 21, +13 to hit with spell attacks). The dragon knows the following spells and can cast them at their lowest levels without material or somatic components:

Cantrips (at will): Lightning Lure, Shocking Grasp, Mage Hand, Spare the Dying

6x/day: Witch Bolt, Chromatic Orb (always chooses lightning damage)

4x/day: Lightning Bolt, Call Lightning

3x/day: Storm Sphere, Chain Lightning

1x/day: Illusory Dragon (always chooses lightning damage) 

Multiattack. The dragon makes four attacks: one with its bite and three with its tail.

Bite. Melee Weapon Attack: +15 to hit, reach 15 ft., one target. Hit: 25 (3d10 + 8) piercing damage plus 30 (5d8) lightning damage.

Tail. Melee Weapon Attack: +15 to hit, reach 20 ft., one target. Hit. 22 (2d12+8) bludgeoning damage.

Cloud Breath (Recharge 5-6). The dragon exhales thick green fog and lightning in a 150ft long, 15ft wide line in front of it. Each creature in that area must make a DC 25 Dexterity saving throw, taking 95 (19d8) lightning damage on a failed save, or half as much damage on a successful one. Creatures who fail the saving throw also suffer effects similar to the slow spell for one minute.

Dash 5x/day. The dragon can take the dash action as a bonus action.

Outmaneuver. The dragon may use its reaction to move up to half its speed when another creature enters its reach. This movement doesn't provoke opportunity attacks.

Static Discharge. When struck with a weapon or spell attack, the dragon unleashes a sphere of devastating lightning from its form. All creatures of the dragon's choosing within fifteen feet must make a DC25 Dexterity saving throw or take 53 (15d6) lightning damage, half on success.