Baron of Hell

Infernal Despair. Each opponent within 15 feet of the Baron of Hell makes saving throws with disadvantage.

Legendary Resistance (3/day). If Baron of Hell fails a saving throw, he can choose to succeed instead. 

Magic Resistance. Baron of Hell has an advantage on savings throws against spell and other magical effects.

Magic Weapons. Baron of Hell's weapon attacks is magical.

Regeneration. Baron of Hell gains 20 hit points at the start of his turn. Baron of Hell dies only if he starts his turn with -21 hit points.

Multiattack. Baron of Hell makes 4 attacks.

Bite. Melee Weapon Attack: +15 to hit, reach 5 ft., 1 target. Hit: 15 (2d6 + 8) piercing  damage. The target must succeed on a DC 22 Con. saving throw or becomes poisoned. While poisoned in this way, the target can't regain hit points,  and it takes (3d6) poison damage at the start of each of its turn. 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: +15 to hit, reach 10 ft., one target. Hit: 17 (2d8+8) slashing damage.  

Fireball. Ranged Weapon Attack: +15 to hit, reach 150 ft., one target. Each creature in a 20-foot-radius sphere centered on that point must make a Dexterity saving throw of 20. A target takes (8d6)+8 fire damage on a failed save, or half as much damage on a successful one. The fire spreads around corners. It ignites flammable objects in the area that aren't being worn or carried.

Teleport. Baron of Hell magically teleports, along with any equipment he is wearing and carrying up to 120 feet to an unoccupied space he can see.

Baron of Hell can take 3 legendary actions. Only one legendary action can be used at a time and only at the end of another creature's turn. Baron of Hell regains spent legendary actions at the start of his turn.

Lightning Storm (Costs 2 Actions). Baron of Hell releases lightning in a 20-foot radius. All other creatures in the area must each make a DC 22 Dex saving throw, taking 18 (4d8) lightning damage on a failed save, or half as much damage on a successful one.

Teleport. Baron of Hell uses his Teleport action.