Lava Keeper

Lava Dribble. Each creature that starts its turn within 5 feet of the lava keeper must make a DC 19 Dexterity saving throw, taking 7 (2d6) fire damage on a failed save, or half as much damage on a successful one.

Innate Spellcasting. The lava keeper's innate spellcasting ability is Wisdom (spell save DC 17). It can innately cast the following spells, requiring no material components: At will: move earth, stone shape 3/day each: wall of fire, wall of stone 1/day each: conjure elemental (earth or fire elemental only), earthquake, fire storm

Multiattack. The lava keeper makes four slam attacks. Alternatively, it can use its Lava Lob twice.

Slam. Melee Weapon Attack: +13 to hit, reach 10 ft., one target. Hit: 25 (4d8 + 7) bludgeoning damage.

Lava Lob. Ranged Weapon Attack: +13 to hit, range 60/240 ft., one target. Hit: 21 (6d6) fire damage, and the target must succeed on a DC 19 Dexterity saving throw or take 10 (3d6) fire damage at the start of its next turn.

Fumarole (Recharge 5-6). The crater between the lava keeper's shoulders erupts in a plume of fire, rock, and toxic smoke. Each creature within 60 feet of the lava keeper must make a DC 19 Constitution saving throw. On a failure, a creature takes 21 (6d6) bludgeoning damage and 21 (6d6) fire damage and becomes poisoned for 1 minute. On a success, a creature takes half the damage and isn't poisoned. A poisoned target can repeat the saving throw at the end of each of its turns, ending the effect on itself on a success. The eruption surrounds the lava keeper in a 20-foot-radius sphere of smoke, considered heavily obscured until the end of its next turn. A wind of moderate or greater speed (at least 10 miles per hour) disperses the smoke.