Cindermite

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

Fire Form. The Cindermite 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 3 (1d6) fire damage. In addition, the elemental can enter a hostile creature's space and stop there. 

Water Vulnerability. When the Cindermite is doused by water, it deals no fire damage until the end of its next turn.

Split. When a Cindermite that has at least 10 hit points remaining takes damage from any source other than water, cold, or wind, it splits into two Cindermites. The new Cindermites occupy the space formerly occupied by the original Cindermite, and each new Cindermite has hit points equal to half the original’s, rounded down.

Heal by Fire. A damaged Cindermite may heal itself by exposing its body to flames (heals 1d4 per round), very hot coals (heals 1d6 per round), or lava (heals 1d8 per round). 

Burning Bite. Melee Weapon Attack: +6 to hit, reach 5 ft., one target. Hit: 5 (1d6 + 2) fire damage. If the target is a creature or a flammable object, it ignites. Until a creature uses an action to pat the flames out, the target takes 3 (1d6) fire damage at the end of each of its turns.

Sacrificial Leap. Ranged Weapon Attack: +4 to hit, range 15/30 ft., one target. Hit: 10 (2d6 + 3) bludgeoning damage plus 5 (1d6 + 2) fire damage. The Cindermite leaps into its victim, exploding itself upon impact. If the attack misses by less than 5, all within 10 feet of the target (except other Cidermites) take half damage unless they make a DEX save (DC14).

Merge. Two damaged Cindermites can combine into one fully healed Cindermite.

Flame Body. If a Cindermite is grappled, it may spend 1 hit point to deal 2d8 fire damage to the grappling creature. The creature must make a strength saving throw (DC 14) to maintain hold of the cinder. This damage may be repeated as an attack every turn.