Magma Mephit

When the mephit dies, it explodes in a burst of lava. Each creature within 5 feet 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.

While the mephit remains motionless, it is indistinguishable from an ordinary mound of magma.

The mephit can innately cast the following spells, requiring no material components:
1/day: heat metal (spell save DC 10)

plus 2 (1d4) fire damage.

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.