Fear Aura. Any creature hostile to the pit fiend that starts its turn within 20 feet of the pit fiend must make a DC 21 Wisdom saving throw, unless the pit fiend is incapacitated. On a failed save, the creature is frightened until the start of its next turn. If a creature's saving throw is successful, the creature is immune to the pit fiend's Fear Aura for the next 24 hours.

Magic Resistance. Avantage on saving throws against spells and other magical effects.

Magic Weapons. The pit fiend's weapon attacks are magical.

Innate Spellcasting. Spellcasting ability is Charisma (spell save DC 21). The pit fiend can innately cast the following spells, requiring no material components:

At will: detect magic, fireball

3/day each: hold monster, wall of fire

Siege Monster. Using the ram like horns on his head, he deals double damage to structures and objects.

Multiattack. The pit fiend makes seven attacks: one with its bite, two with its claw, two with its mace, one with its wings, and one with its tail.

Bite. Melee Weapon Attack: +14 to hit, reach 5 ft., one target. Hit: 22 (4d6 + 8) piercing damage. The target must succeed on a DC 21 Constitution saving throw or become poisoned. While poisoned in this way, the target can't regain hit points, and it takes 21 (6d6) poison damage at the start of each of its turns. The poisoned target can repeat the saving throw at the end of each of its turns, ending the effect on itself on a success.

Claw. Melee Weapon Attack: +14 to hit, reach 10 ft., one target. Hit: 17 (2d8 + 8) slashing damage.

Mace. Melee Weapon Attack: +14 to hit, reach 10 ft., one target. Hit: 15 (2d6 + 8) bludgeoning damage plus 21 (2d6) fire damage.

Tail. Melee Weapon Attack: +14 to hit, reach 10 ft., one target. Hit: 24 (3d10 + 8) bludgeoning damage.

Wing. Melee Weapon Attack: +14 to hit, reach 10ft., one target. Hit: 24 (2d6+8)

Ram. Melee Charge Attack: +14 tot hit, straight line attack, any in a 20 foot line. Hit: 8d6+8

Hellish Rebuke. Rebuke your target by scorching them with 3d10 scorching damage