Magma Mephit

The mephit can innately cast heat metal (spell save DC 10), requiring no material components. Its innate spellcasting ability is Charisma.

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

Melee Weapon Attack: +3 to hit, reach 5 ft.. Hit: 3 (1d4 + 1) slashing plus 2 (1d4) fire damage.

Recharge 6. The magma 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.