Warforged Dragon

Constructed Dragon. The steam dragon does not require air, food, drink, or sleep.

Legendary Resistance 4 a day: if the creature fails a saving throw in can choose to succeed instead.

Steam Canisters (Recharge System).
The dragon has 3 steam canisters mounted along its back. Certain abilities consume canister. Canisters can be targeted and destroyed, causing an explosion dealing 26(4d12) force damage, forcing a DC 18 dexterity saving throw from the attacker. Takes full damage on fail. No explosion happens if canister is empty.
• When all canisters are expended, the dragon cannot use Steam Breath or Overpressure Vent.
• In its lair, the dragon can refuel 1 canister per round (see Lair Actions).
• Outside its lair, it regains all canisters after finishing a long rest.

Heated Plating.
A creature that hits the dragon with a melee attack while within 5 feet takes 7 (2d6) fire damage.

Magic Resistance.
The dragon has advantage on saving throws against spells and other magical effects.

Multiattack.
The dragon makes three attacks: one with its bite and two with its claws.

Bite. Melee Weapon Attack: +12 to hit, reach 10 ft., one target.
Hit: 19 (2d10 + 7) piercing damage plus 7 (2d6) fire damage.

Claw. Melee Weapon Attack: +12 to hit, reach 5 ft., one target.
Hit: 15 (2d6 + 7) slashing damage.

Tail. Melee Weapon Attack: +12 to hit, reach 15 ft., one target.
Hit: 17 (2d8 + 7) bludgeoning damage, and the target must succeed on a DC 19 Strength saving throw or be knocked prone.

Steam Breath (Costs 1 Canister)

Can use all three breaths in a row without recharging. to refuel while empty must roll a 19-20 to refuel 1.

The dragon exhales superheated steam in a 60-foot cone.
Each creature in that area must make a DC 19 Constitution saving throw, taking 54 (6d8) fire damage  and (6d8) on a failed save, or half as much on a success.

On a failed save, a creature is also Blinded until the end of its next turn as scalding vapor fills its eyes and lungs.

Overpressure Vent (Costs 1 Canister)

The dragon vents steam violently from its back.

Creatures of the dragon’s choice within 15 feet must succeed on a DC 19 Strength saving throw or take 22 (2d10) acid damage and (2d10) fire then be pushed 20 feet away and knocked prone.
On a success, a creature takes half damage and isn’t pushed or knocked prone.

Pounce. If the dragon has more than half its movement available, it can pounce towards a target. Target must make a DC 18 dexterity saving throw or be knocked prone.

The warforged steam 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.

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

Tail Attack. The dragon makes a tail attack.

Canister Surge (Costs 2 Actions).
The dragon immediately regains 1 expended steam canister and sheds scalding vapor. Creatures within 10 feet take 10 (3d6) fire damage.