Death Burst. When the mephit dies, it explodes in a burst of lava. Each creature within 5 ft. of it must make a DC 11 Dexterity saving throw, taking 7 (2d6) fire damage on a failed save, or half as much damage on a successful one.
False Appearance. While the mephit remains motionless, it is indistinguishable from an ordinary mound of magma.
Innate Spellcasting (1/Day). The mephit can innately cast heat metal (spell save DC 10), requiring no material components. Its innate spellcasting ability is Charisma.
Claws. Melee Weapon Attack: +3 to hit, reach 5 ft., one creature. Hit: 3 (1d4 + 1) slashing damage plus 2 (1d4) fire damage.
Fire Breath. The mephit exhales a 15-foot cone of fire. Each creature in that area must make a DC 11 Dexterity saving throw, taking 7 (2d6) fire damage on a failed save, or half as much damage on a successful one.
Variant: Summon Mephits. The mephit has a 25 percent chance of summoning 1d4 mephits of its kind. A summoned mephit appears in an unoccupied space within 60 feet of its summoner, acts as an ally of its summoner, and can't summon other mephits. It remains for 1 minute, until it or its summoner dies, or until its summoner dismisses it as an action.