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

Curse Regeneration. The curse regains all it's lost hit points at the start of it's turn. If the curse is stunned, unconscious, prone, grappled, restrained, or incapacitated, this trait doesn’t function at the start of it's turn.

Infernal Aura. Any creature hostile to the curse that starts its turn within 30 feet must make a DC 18 Constitution saving throw, unless the curse is incapacitated or stunned. On a failed save, the creature starts burning. While burning this way, those creatures can't regain hit points and take 21 (6d6) fire damage at the start of each of their turns. Creatures can repeat the saving throw at the end of each of their turns, ending the effect on themselves on a success.

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

Magic Weapons. The curse's weapon attacks are magical.

Unarmed Strike. Melee Weapon Attack: +14 to hit, reach 5 ft., one target. Hit: 16 (2d10 + 5) bludgeoning damage plus 15 (5d4 + 2) fire damage.

Disaster Flames. Melee Weapon Attack: +14 to hit, reach 5 ft., one target. Hit: 24 (3d10 + 8) bludgeoning damage plus 21 (6d6) fire damage. If the target is a creature, they must succeed a DC 18 Constitution saving throw or become blinded and burning for 1 minute.

Ember Insects. Ranged Weapon Attack: +14 to hit, reach 5-50ft., one target. Hit: 33 (2d12 + 20) fire damage.

Flashstep. The curse dashes so quickly it seems as though it teleports, along with any equipment it is wearing or carrying, up to 120 feet to an unoccupied space it can see.

Maximum: Meteor. Once per battle, the curse may summon a meteor to fall from the atmosphere. Each creature in a 40-foot-radius sphere centered on itself must succeed a DC 20 Dexterity saving throw. A creature takes 75 (20d6 + 6) fire damage and 75 (20d6) bludgeoning damage on a failed save, or half as much damage on a successful one. 

Unarmed Strike. The curse may use it's bonus action to make an unarmed strike attack.

Domain Amplification. The curse may use a bonus action to amplify it's next attack with a domain's sure-hit effect, attacking with advantage and a +6 to the roll.

Domain Expansion: Coffin of the Iron Mountain. Once per battle, when the curse is reduced to 0 hit points, it can choose to drop to 1 hit point instead using it's reaction. Then itself and each creature of the curse's choice within 120 feet of it are brought into it's domain. While in the domain, the curse's weapon attacks have infinite range and may target each creature within the domain. The effects of the domain end after 3 minutes or if the curse is killed.

The curse 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. The curse regains spent legendary actions at the start of its turn.

Attack. The curse makes one unarmed strike attack or one ember insects attack.

Move. The curse moves up to half its speed.

Flashstep (Costs 2 actions). The curse uses it's flashstep.