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

Magic Weapons. Zephros weapon attacks are magical.

Innate Spellcasting. Zephros spellcasting ability is Charisma (spell save DC 19). The pit fiend can innately cast the following spells, requiring no material components:

At Will: Fire Bolt   (5th Level)

3/day: fireball, wall of fire

Fiend General: as a bonus action, Zephros gets 3 summons of increasing difficulty a day. He has to go through 1 summon to get to the next summon. after using a summon, he cant use it again.

1st summon: 4 imps

2nd summon: 3 hell hounds

3rd summon:  2 Cambions

Multiattack. Zephros makes 2 attacks

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 (6d6) fire damage.

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