Cinder King-Armored

The Black Torch. The Cinder King's attacks are treated as magical for the purpose of bypassing resistance and immunity to nonmagical weapons.

Fire Aura. At the start of each of The Cinder King’s turns, each creature within 10 feet of it takes 17(5d6) fire damage, and flammable objects in the aura that aren’t being worn or carried ignite. A creature also takes 17 (5d6) fire damage if it touches The Cinder King or hits it with a melee attack while within 10 feet of it. Nonmagical weapons that hit The Cinder King are melted by the intense fire immediately after dealing damage with them.

Fiery Regeneration: The Cinder King heals for 10 at the end of each of his turns. Taking cold damage stops this effect until his next turn.

Illumination. The Cinder King sheds bright light in a 30-foot radius and dim light in an additional 30 feet.

Water Susceptibility. For every 5 feet The Cinder King moves in water, or for every gallon of water splashed on it, it takes 1 cold damage.

Innate Spellcasting. Amalgam of Fire’s innate spellcasting ability is Charisma (spell save DC 19, +12 to hit with spell attacks). It can innately cast the following spells, requiring no material components:

At will:  fireball, wall of fire

3/day: fire storm

1/day: meteor swarm

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

Legendary Resistance (3/Day). If The Cinder King fails a saving throw, he can choose to succeed instead.

Multiattack. The Cinder King makes two Black Torch attacks or one Black Torch attack and one Eruption attack.

Black Torch. Melee Weapon Attack: +12 to hit, reach 10 ft., one target. Hit: 18 (2d10 + 7) bludgeoning damage plus 18 (5d6) fire damage. If the target is a creature or a flammable object, it ignites. Until a creature takes an action to douse the fire, the target takes 5 (1d10) fire damage at the start of each of its turns.

Eruption. The Cinder King can choose one creature within 120 feet that it can see, and make the ground erupt from under them. The target must succeed in a DC 19 Dexterity saving throw or take 28(8d6) fire damage and be knocked prone. 

Summon Elementals (1/Day). The Cinder King summons up to ten fire elementals. Summoned elementals have maximum hit points, appear within 100 feet of The Cinder King, and disappear if The Cinder King is reduced to 0 hit points.

The Cinder King has 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 Cinder King regains spent legendary actions at the start of his turn.

At-Will Spell (Costs 1 Action). The Cinder King casts one of his at-will spells.

Fiery Teleport (Costs 1 Action). The Cinder King teleports to a location he can see within 120 feet, and causes every creature within it's Fire Aura at the new location to the the damage of the Aura.

Summon Orb of Flame (Cost 2 Actions). The Cinder King creates an Orb of Flame with 1 hit point and 5 AC. At initiative 0 it gains a token and grows, starting at 0 tokens. When it dies, or reaches 10 tokens, it deals 2d6 fire damage for each token(Dex DC 16 Half)

Ignite (Costs 3 Actions).  The Cinder King causes one creature it can see within 30 feet of it to burst into flames. The target must make a DC 19 Constitution saving throw. On a failed save, the target takes 70 (20d6) fire damage and catches fire. A target on fire takes 10 (3d6) fire damage when it starts its turn, and remains on fire until it or another creature takes an action to douse the flames. On a successful save, the target takes half as much damage and doesn’t catch fire.

At half health, the Cinder King's armor melts off as the Fire Aura increased to 20(6d6), his AC drops to 15, walk speed increases to 35 and his regeneration increases to 15. These effects last until the end of combat.