Inflamer. The elemental has abilities which magically inflame areas. These flames stand 5 feet tall, last for 1 minute, and do not spread. A creature takes 5 (1d10) fire damage when it enters a flaming area for the first time on a turn or starts its turn there. A creature occupying a space when it becomes inflamed must make a DC 15 Dexterity saving throw. On success, the creature moves to an adjacent space of its choice.

Igniter. The elemental has abilities which ignite creatures or objects. Until someone takes an action to douse the fire, the ignited target takes 5 (1d10) fire damage at the start of each of its turns.

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 5 (1d10) 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 5 (1d10) fire damage and ignites. 

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

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

Cooldown. If the elemental takes cold damage, it can't ignite targets until the end of its next turn.

Multiattack. The elemental makes two touch attacks. If both attacks hit the same target, the target's space is inflamed.

Touch. Melee Weapon Attack: +6 to hit, reach 5 ft., one target. Hit: 10 (2d6 + 3) 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.

Erupt (Recharge 4-6). The elemental explodes outward in a 10 foot radius. Each creature in the area must succeed on a DC 15 Dexterity saving throw or take 13 (2d12) fire damage and be ignited. On a successful save, the creature takes half as much damage and isn't ignited.

Flamespit. As a bonus action, the elemental can spit a gout of flame at a space within 30 feet of it, inflaming it.

Magical Ignition. When the elemental takes damage from a spell of magical weapon, it inflames three spaces of its choice within 10 feet of it.

Each round, the elemental takes a new legendary action at the end of another creature's turn as indicated in the name of the legendary action. After the third round, the elemental can take one legendary action of its choice per round for the rest of combat.

Round 1: Blazing Blitz. The elemental burns white hot and moves up to its speed. Each space that it moves through becomes inflamed.

Round 2: Pyrolash. The elemental extends a massive tendril of flame from its body and slams it to the ground, forming a line of flame 30 feet long and 5 feet wide in a direction of the elemental's choice. Each creature in the line takes 5 (1d10) fire damage and each space in the line becomes inflamed.

Round 3: Conflagration. The elemental magically increases the ferocity of its flames. Each ignited creature or object takes 5 (1d10) fire damage. Each space within 5 feet of an inflamed area melts, becoming difficult terrain, and any creature in one of these spaces must make a DC 15 Constitution saving throw, taking 5 (1d10) fire damage for each adjacent inflamed area on a failed save or half as much damage on a successful one. Each inflamed area is extinguished and each ignited target is extinguished.