Fire Form. The elemental can move through a space as narrow as 1 inch wide without squeezing. A creature that touches the elemental or hits it with a melee attack while within 5 feet of it takes 11 (2d10) fire damage. In addition, the elemental can enter a hostile creature's space and stop there. The first time it enters a creature's space on a turn, that creature takes 11 (2d10) fire damage and catches fire; until someone takes an action to douse the fire, the creature takes 11 (2d10) fire damage at the start of each of its turns.

Illumination. The elemental sheds bright light in a 30-foot radius and dim light in an additional 30 feet. The elemental can choose to stop glowing or start glowing again.

Water Susceptibility. For every 10 feet the elemental moves in water, or for every 2 gallons of water splashed on it, it takes 1 cold damage.

Innate Spellcasting. The elemental's innate spellcasting ability is Constitution (spell save DC 16, +8 to hit with spell attacks). It can innately cast the following spells, requiring no material components:

At will: fire bolt, pyrotechnics

1/day each: fireball, immolation.

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

Multiattack. The elemental makes three touch attacks. It can replace of of these touch attacks with a Smoke Burst attack.

Touch. Melee Weapon Attack: +8 to hit, reach 5 ft., one target. Hit: 13 (2d8 + 4) 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 11 (2d10) fire damage at the start of each of its turns.

Smoke Burst. The elemental fires a blast of thick, super-heated smoke in a 15 foot cone. This cone of smoke lasts for a minute or until a wind of strong or greater speed (at least 20 miles per hour) disperses it, and is heavily obscured. Additionally, when a creature enters the smoke for the first time (including when his action is used) or ends their turn in the smoke, they tale 7 (2d6) fire damage. 

The elemental can see through the smoke created by this action. 

Blazing Inferno (Recharge 6). The elemental explodes in a burst of flames. All creatures in a 30 foot sphere centered on the elemental must make a DC 16 dexterity saving throw, taking 36 (8d8) fire damage. fire damage on a failed save, or half as much on a success. The fire spreads around corners. Creatures and flammable objects in the sphere ignite. Until a creature takes an action to douse the fire, creatures ignited in this way take 11 (2d10) fire damage at the start of each of their turns.