Crimson Flame

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 catches fire; until someone takes an action to douse the fire, the creature takes 5 (1d10) 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.

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.

Innate Spellcasting. The elemental's spellcasting ability is Charisma (spell save DC 14). The elemental can innately cast the following spells, requiring no material components:

At will: prestidigitation, thaumaturgy, detect magic, silent image

4/day each: augury, fireball, dispel magic, suggestion, polymorph

Multiattack. The elemental makes two touch attacks. It can use blast of flame instead of its touch attacks.

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.

Blast of Flame. Ranged Spell Attack: +6 to hit, range 30ft., 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.

Invisibility. The elemental magically turns invisible until it attacks or until its concentration ends (as if concentrating on a spell). Any equipment the elemental wears or carries is invisible with it.

Etherealness. The elemental enters the Ethereal Plane from the Material Plane, or vice versa. It is visible on the Material Plane while it is in the Border Ethereal, and vice versa, yet it can't affect or be affected by anything on the other plane.

Possession (Recharge 6). One humanoid that the elemental can see within 5 feet of it must succeed on a DC 13 Charisma saving throw or be possessed by the elemental; the elemental then disappears, and the target is incapacitated and loses control of its body. The elemental now controls the body but doesn't deprive the target of awareness. The elemental can't be targeted by any attack, spell, or other effect, except ones that turn undead, and it retains its alignment, Intelligence, Wisdom and Charisma. It otherwise uses the possessed target's statistics, but doesn't gain access to the target's knowledge, class features, or proficiencies.

The possession lasts until the body drops to 0 hit points, the elemental ends it as a bonus action, or the elemental is turned or forced out by an effect like the dispel evil and good spell. When the possession ends, the elemental reappears in an unoccupied space within 5 feet of the body. The target is immune to this elemental's Possession for 24 hours after succeeding on the saving throw or after the possession ends.