Archagon

Diabolical Restoration. If the devil dies outside the Nine Hells, its body disappears in sulfurous smoke, and it gains a new body instantly, reviving with all its Hit Points somewhere in the Nine Hells.

Magic Resistance. The devil has Advantage on saving throws against spells and other magical effects while in the Nine Hells or when it is within 60 feet of another CR 9+ devil.

True Name. If a creature the devil can hear within 60 feet of it speaks the devil's True Name aloud, the devil loses its damage Resistances, damage Immunities, and Devilish Charm Reaction for 24 hours.

Multiattack. The archagon makes two Infernal Pike attacks.

Infernal Pike. Melee Attack Roll: +7, reach 10 ft. Hit: 9 (1d10 + 4) Piercing damage plus 11 (2d10) Fire damage, and the archagon chooses one of the following effects:

Focused Hate. The target has Disadvantage on attack rolls made against creatures other than the archagon until the end of the archagon's next turn.

Hellbite. The target takes an extra 5 (2d4) Fire damage.

Skewer. The legate deals 5 (1d10) Piercing damage plus 5 (1d10) Fire damage to another creature within 5 feet of the target.

Devilish Charm (1/Day). Trigger: The devil is targeted by an attack, spell, or other magical effect by a creature it can see within 60 feet. Response -- Charisma Saving Throw: DC 15, the triggering creature. Failure: The target is Charmed until the start of the creature’s next turn, and the devil chooses a new target the devil can see for the triggering effect. The new target must be within the triggering effect’s range.