Traits

Death Throes: When the balor dies, it explodes, and each creature within 30 feet of it must make a DC 20 Dexterity saving throw, taking 70 (20d6) fire damage on a failed save, or half as much damage on a successful one. The explosion ignites flammable Objects in that area that aren't being worn or carried, and it destroys the balor's Weapons.

Fire Aura: At the start of each of the balor's turns, each creature within 5 feet of it takes 10 (3d6) fire damage, and flammable Objects in the aura that aren't being worn or carried Ignite. A creature that touches the balor or hits it with a melee Attack while within 5 feet of it takes 10 (3d6) fire damage.

Magic Resistance: The balor has advantage on Saving Throws against Spells and other magical Effects.

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

Actions

Multiattack: The balor makes two attacks: one with its Longsword and one with its whip.

Longsword: Melee Weapon Attack: +14 to hit, reach 10 ft., one target. Hit: 21 (3d8 + 8) slashing damage plus 13 (3d8) lightning damage. If the balor scores a critical hit, it rolls damage dice three times, instead of twice.

Whip: Melee Weapon Attack: +14 to hit, reach 30 ft., one target. Hit: 15 (2d6 + 8) slashing damage plus 10 (3d6) fire damage, and the target must succeed on a DC 20 Strength saving throw or be pulled up to 25 feet toward the balor.

Teleport: The balor magically teleports, along with any Equipment it is wearing or carrying, up to 120 feet to an unoccupied space it can see.

Variant: Summon Demon (1/Day): The demon chooses what to summon and attempts a magical summoning.
A balor has a 50 percent chance of summoning 1d8 vrocks, 1d6 hezrous, 1d4 glabrezus, 1d3 nalfeshnees, 1d2 mariliths, or one Goristro.
A summoned demon appears in an unoccupied space within 60 feet of its summoner, acts as an ally of its summoner, and can't summon Other Demons. It remains for 1 minute, until it or its summoner dies, or until its summoner dismisses it as an action.