Fear Aura. Any creature hostile to Bel that starts its turn within 20 feet of him must make a DC 23 Wisdom saving throw, unless Bel is incapacitated. Unless the save succeeds, the creature is frightened until the start of its next turn. If a creature's saving throw is successful, the creature is immune to Bel's Fear Aura for the next 24 hours.

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

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

Magic Weapons. Bel's weapon attacks are magical.

Innate Spellcasting. Bel's spellcasting ability is Charisma (spell save DC 23). Bel can innately cast the following spells, requiring no material components:

At will: detect magic, fireball

1/day each: imprisonment, meteor swarm

3/day each: dispel magic, hold monster, mirror image, mislead, raise dead, teleport, wall of fire

Multiattack. Bel makes three attacks: two with his greatsword and one with his tail.

Greatsword. Melee Weapon Attack: +16 to hit, reach 10 ft., one target. Hit:23 (4d6 + 9) slashing damage plus 21 (6d6) fire damage. If the target is a flammable object that is not being held or worn, it catches fire.

Tail. Melee Weapon Attack: +16 to hit, reach 10 ft., one target. Hit:25 (3d10 + 9) bludgeoning damage. If the target is a creature, it must succeed on a DC 23 Constitution saving throw or be stunned until the end of its next turn.

Fireball. Bel casts fireball.

Tactical Edge (Costs 2 Actions). Roll a d6 for Bel. The number rolled on the die is subtracted from the next attack roll made against Bel or an ally of his choice within the next minute.

Summon Ice Devil (Costs 3 Actions). Bel magically summons an ice devil with an ice spear (as described in the ice devil's entry in the Monster Manual). The ice devil appears in an unoccupied space within 60 feet of Bel, acts as Bel's ally, and can summon other devils if it has such power. The ice devil remains until Bel dies or until he dismisses it as an action.