Magmin

Death Burst. When the magmin dies, it collapses into a Tiny cinder cone. On initiative count 20 after the magmin dies, the cinder cone erupts in a burst of fire and lava. Each creature within 10 feet of the cone must make a DC 11 DEX save, taking 7 (2d6) fire damage on a failed save, or half as much damage on a successful one. Flammable objects that aren't being worn or carried in that area are ignited.

Hardened Magma. While the magmin isn't ablaze, it is resistant to piercing and slashing damage from nonmagical attacks, and it is vulnerable to thunder damage.

Molten Body. While the magmin is ablaze, each creature that hits it with a melee attack while within 5 feet of it takes 3 (1d6) fire damage.

Burning Slam. _Melee Weapon Attack:_ +4 to hit, reach 5 ft., one target. _Hit:_ 4 (1d4+2) bludgeoning damage plus 3 (1d6) fire damage.

Ignited Illumination. The magmin sets itself ablaze or extinguishes its flames. While ablaze, the magmin sheds bright light in a 10-foot radius and dim light for an additional 10 feet.