Innate Spellcasting. The dragon's innate spellcasting ability is Wisdom (spell save DC 16). The oni can innately cast the following spells, requiring no material components:

At will: control flames, create or destroy water, bane

1/day each: heat metal, suggestion, erupting earth, darkness (20-ft sphere)

Multiattack. The dragon makes three attacks: one with its bite and two with its claws.

Bite. Melee Weapon Attack: +10 to hit, reach 10 ft., one target. Hit: 17 (2d10 + 6) piercing damage + 3 (1d6) fire damage + 2 (1d4) poison damage.

Claw. Melee Weapon Attack: +10 to hit, reach 5 ft., one target. Hit: 13 (2d6 + 6) slashing damage.

Fire Breath (Recharge 5–6). The dragon exhales fire in either a 30-foot cone or a 60-ft line that is 10 feet wide. Each creature in that area must make a DC 18 Dexterity saving throw, taking 58 (16d6 + 2) fire damage on a failed save, or half as much damage on a successful one.