Clockwork Dragon: Reforged

Mechanical Menace: Crafted of Mithril and Orichalchum, the Clockwork dragon resists all non Lightning damage.

Superheated Metal: The Clockwork Dragon's Chassis is burning to the touch, and ending your turn/entering a square within 5 feet of the Dragon deals 4d8 Fire Damage.

Arcane Engine: Once per turn as a free action, the Clockwork Dragon can change the magical damage type associated with its attacks.

Mana pool: Each of the Clockwork Dragon's abilities use some of its Health as fuel. Due to this design flaw, the Clockwork Dragon has Obscene amounts of health.

Multi-attack: Clockwork Dragon Makes three attacks with its claws, and two bite attacks.

Mystical Claw: Melee Weapon Attack: +14 to hit, reach 10 ft., 1 target. Hit: 40 (4d10 + 20) [Slashing,] (Lightning, Fire, Cold, Necrotic, Radiant, Acid, Poison.) damage. Costs 20 HP

Enchanted Bite Melee Weapon Attack: +14 to hit, range 5 ft, 1 target. Hit: 50 (6d10 + 20) [Piercing, Crushing] (Lightning, Fire, Cold, Necrotic, Radiant, Acid, Poison.) damage. Costs 20 HP.

Tail Slap: Melee Weapon Attack: +14 to hit, range 30 ft, 3 targets. Hit: 65 (10d10 +15)
(Crushing) (Lightning, Fire, Cold, Necrotic, Radiant, Acid, Poison) damage. Enemies hit with Tail slap are knocked prone, and pushed up to 20 ft. Costs 25 HP.

Arcane Cannon: Breath Weapon Attack, Dexterity save DC 20, Cone 20ft by 60 ft. Hit: 80 (16d10) (Lightning, Fire, Cold, Necrotic, Radiant, Acid, Poison) damage. 1/2 Damage on a successful save. Different bonus effect depending on Element. Cooldown 3 Rounds. Costs 40 HP.

Lightning: On failed save, Target is paralyzed for one round.
Fire: On failed save, Target takes 8d6 fire damage at the start of their next turn, double this if they are wearing metal equipment.
Necrotic: On failed save, Target is slowed, and cannot cast leveled spells for one round.
Radiant: On failed save, Target is blinded for one round.
Acid: On failed save, Targets equipment is damaged, and cannot be used until they spend an action to repair it.
Poison: On failed save, target takes 4d8 poison damage at the start of their turn for the next three rounds.

Charging the Cannon: The Arcane Cannon comes off of cooldown, regardless of how much time was left. This costs 100 HP.

Arcane Super Charge: The Clockwork Dragon can take an extra action during this turn. This costs 150 HP. 

Eldritch Shield: The Clockwork Dragon becomes immune to Magical Damage or Magical Effects for one round. This costs 200 HP. The HP paid can stack a total of 3 times. After "Nuclear Option" is activated, Eldritch shield lasts for two rounds for every usage.

Shimmering Scales: 3/day. If the Clockwork Dragon would be affected by a spell or magical effect, the spell/effect is now reflected on the caster. Original rules of the spell still apply. Costs 50 HP.

Steam Vent: 3/day. If the Clockwork Dragon takes damage from a melee attack/ability/spell, the target must make a CON Save, DC 19. Damage 8d6, 1/2 that on success. Costs 50 HP.

Energy Drain: 4/day, If the Clockwork Damage is targeted by an attack, spell, or ability, it can drain Up to 2 Spell slots of Level 7 or lower, 3 Ki points, or 3 sorcery points from the target. The clockwork dragon then restores 100 HP. The attack/spell/ability go through normally following this effect. 

Mordenkainen's Mistake: 2/day, Consumes an entire turn. AOE Magical Attack, Radius 35 feet around the Clockwork Dragon. Dex Save DC 21. Hit: (20d12) (Lightning, Fire, Cold, Necrotic, Radiant, Acid, Poison) damage. This attack cannot bring enemies below 1 health. The same effects of the Breath Weapon Elements apply. After using this ability, The Clockwork Dragon is stunned, and has no damage resistance until the start of its next turn. Cost 300 HP.

Nuclear Option: 1/day, 1 action. Usable once Clockwork Dragon is below 50% health. The Clockwork dragon's Arcane Engine enters a supernova Stage. Abilities for the Clockwork Dragon no longer consume HP, and cannot be resisted. However, the Clockwork Dragon's mithril scales have melted, removing all damage resistance from the Clockwork Dragon.

Destined Defeat: 3/day, Reaction. The target's roll is changed to a 1. costs 200 HP.

Mystical Superiority: 3/day, Reaction. if the Clockwork dragon would fail a saving throw, it instead succeeds. Costs 50 HP.

Arcane Rockets: 5/day, Bonus Action. Clockwork Dragon Casts Two instances of Magic missile at 9th level. Costs 100 HP. Can cast a third volley of Magic Missile at the cost of 50 more HP. Once "Nuclear Option" has activated, Every cast of Magic Missiles uses three volleys. Cannot be resisted, and does additional elemental damage based on the Clockwork Dragon's current element. (One volley of Magic Missiles does 36+10 damage)