Bel

Magic Weapons. The balor's weapon attacks are magical.

Legendary Resistance (3/Day). If Bel fails a saving throw, he can choose to succeed instead.

Superiority Dice. Bel has eight Superiority Dice, which are d10s. He regains them all after a short or long rest.

Innate Spellcasting. Bel's spellcasting ability is Charisma (spell save DC 22). Bel can innately cast the following spells, requiring no material components:
At-Will: Detect Magic, Fireball
3/day each: Hold Monster, Wall of Fire

Greatsword. Melee Weapon Attack: +10 to hit, reach 10 ft., one target. Hit: 18 (3d6 + 8) slashing damage plus 3 (1d6) fire damage.

Call Reinforcements.  Summon 1d4 Imp from Avernus to serve him. Imps take their turn on 20 initiative, losing to ties.

Legendary Parry: Bel expends a Superiority Die and enters a defensive stance. The next attack roll made against him (including ranged and spell attacks) before the beginning of his next turn takes a penalty on the attack roll equal to the result shown on the die.

Legendary Riposte: Bel can only trigger this Legendary Action at the end of a creature's turn that missed him with a melee attack and is still within 10ft of him. He makes an attack with his greatsword against that creature. If he hits, he expends a Superiority Die and adds its result to the damage. In addition, if the target is Huge or smaller, they must make a Strength saving throw (DC 23) or be knocked up to 30ft away and land prone.

Legendary Sweeping Attack: Bel makes an attack with his greatsword. If he hits, he expends a Superiority Die. All foes within 10ft that have an Armor Class low enough to be struck by his initial attack roll take damage equal to the number rolled on Bel's Superiority Die

Sudden Demotion!: Bel drains the life of one Imp under his command within 60ft. Bel absorbs the released soul energy, gaining a second wind that heals him for 1d10 hit points,  restoring one of his spent Superiority Dice, and regaining one daily use of his Legendary Resistance ability, making him ever-more indomitable.

Sudden Promotion!: Bel infuses two Imps with fiendish energy and converts them into one Spined Devil. He can also combine two Spined Devils to make one Barbed Devil.