Magic Resistance. The dragon has advantage on saving throws against spells and other magical effects.

Innate Spellcasting. The dragon's innate spellcasting ability is Charisma. It can innately cast the following spells (spell save DC 17, +9 to hit with spell attacks), requiring no material components:

At will: charm person, detect magic, disguise self, fire bolt (4d10)

2/day each: dispel magic, invisibility, suggestion

1/day each: divine word, plane shift

Multiattack. The dragon can use its Frightful Presence. It then makes one Bite attack and two Claw attacks.

Bite. Melee Weapon Attack: +11 to hit, reach 10 ft., one target. Hit: 17 (2d10 + 6) piercing damage plus 5 (1d10) fire damage.

Claw. Melee Weapon Attack: +11 to hit, reach 5 ft., one target. Hit: 13 (2d6 + 6) slashing damage.

Frightful Presence. Each creature of the dragon's choice that is within 120 feet of the dragon and aware of it must succeed on a DC 17 Wisdom saving throw or become frightened for 1 minute. A creature can repeat the saving throw at the end of each of its turns, ending the effect on itself on a success. If a creature's saving throw is successful or the effect ends for it, the creature is immune to the dragon's Frightful Presence for the next 24 hours.

Hellfire Breath (Recharge 5–6). The dragon exhales hellfire in a 60-foot cone. Each creature in that area must make a DC 19 Constitution saving throw. On failed save, a creature takes 60 (11d10) fire damage and becomes vulnerable to fire damage until the end of its next turn. On a successful save, a creature takes half as much damage and suffers no other effects.

Change Shape. The dragon magically polymorphs into a tiefling or any Medium-sized devil. It can revert to its true form as a bonus action. Its statistics, other than its size, are the same in each form. Any equipment it is wearing or carrying isn’t transformed. It reverts to its true form if it dies.