Cherufe

Death Burst. When Cherufe dies, it explodes in a burst of fire and magma. Each target within 60 feet of it must make a DC 20 Dexterity saving throw, taking 56 (16d6) 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.

Earth Glide. Cherufe can burrow through earth, stone, and lava/magma. While doing so, it doesn’t disturb the material it moves through.

Fire Aura. At the start of each of the Cherufe’s turns, each creature within 10 feet of it takes 10 fire damage, and flammable objects in the aura that aren’t being worn or carried ignite. A target that touches Cherufe or hits it with a melee attack while within 10 feet of it takes 10 fire damage.

Freedom of Movement. Cherufe ignores difficult terrain, and magical effects can’t reduce its speed or cause it to be restrained. It can spend 5 feet of movement to escape from nonmagical restraints or being grappled.

Illumination. Cherufe sheds bright light in a 30-foot radius and dim light for an additional 60 feet.

Legendary Resistance (1/Day). If Cherufe fails a saving throw, it can choose to succeed instead. 

Regeneration. Cherufe regains 10 hit points at the start of its turn as long as it is on the Plane of Fire, Earth, or a Para-Elemental plane between the two. If it takes cold damage, this trait doesn’t function at the start of its next turn. It dies/is destroyed only if it starts its turn with 0 hit points and doesn’t regenerate.

Siege Monster. Cherufe deals double damage to objects and structures. 

Summon Mephits (1/Day). Cherufe can use an action to summon 2d4 magma mephitis within 30 feet.

Water Susceptibility. For every 5 feet it moves in water, or for every gallon splashed on it, Cherufe takes 5 cold damage.

Multiattack. Cherufe makes three slam attacks.

Slam. Melee Weapon Attack: +12 to hit, reach 10 ft., 1 target. Hit: 19 (2d12 + 6) bludgeoning damage plus 7 (2d6) fire damage.

Magma Pillar. Each creature within a 15-foot radius, 30-foot high cylinder centered on a point within 60 feet must make a DC 16 Dexterity saving throw, taking 28 (8d6) fire damage on a failed save, or half as much on a success. Flammable objects not being worn or carried in the cylinder ignite.