Be'lakor, The Dark Master

Legendary Resistance (5/Day). If Be’lakor fails a saving throw, he can choose to succeed instead.

Shadow Form. Be’lakor is immune to any spell or effect that would change his form. Additionally, while Be’lakor is in darkness, he is invisible. Be’lakor’s weapon attacks are magical.

Shadow Lord. Whenever an attack is made against Be’lakor by a creature that is more than 60 feet away from him, that attack is made with disadvantage.

Lord of Torment. Whenever a creature within 60 feet of Be’lakor becomes Frightened, Be’lakor regains 3d10 hit points. Creatures that are hostile to Be’lakor within 30 feet of him have disadvantage on saving throws against being frightened.

Spiteful Jealousy. Be’lakor has advantage on attack rolls made against Fiends.

Magic Resistance. Be’lakor has advantage on saving throws against spells and magical effects.

Being of Shade. Be’lakor can move through other creatures and objects as if they were difficult terrain. He takes 1d10 Force damage if he ends his turn inside of an object. 

Black Lightning. If Be’lakor is reduced to 0 hit points, he explodes, letting out dark lightning. Every creature within 30 feet of Be’lakor when this happens must make a DC 27 Dexterity saving throw, taking 12d10 Lightning damage and 1d4 Force damage on a failed save or half as much on a successful one.

Spellcasting. Be’lakor is a 20th level spellcaster. His spellcasting ability is Charisma (spell save DC 27, +19 to hit with spell attacks). Be’lakor can cast the following spells:

Cantrip (At will) Mind Sliver, Mage Hand, Message, Thaumaturgy, Prestidigitation

1st level (4 slots) Bane, Cause Fear, Charm Person, Detect Evil and Good, Detect Magic, Dissonant Whispers, Silent Image

2nd level (3 slots) Blur, Detect Thoughts, Enlarge/Reduce, Enthrall, Shadow Blade, Suggestion, Ray of Enfeeblement, Vortex Warp

3rd level (3 slots) Counterspell, Dispel Magic, Fear, Gaseous Form, Hunger of Hadar, Lightning Bolt, Major Image, Summon Lesser Daemons, Remove Curse

4th level (3 slots) Blight, Charm Monster, Compulsion, Confusion, Evard’s Black Tentacles, Fabricate, Phantasmal Killer

5th level (3 slots) Cloudkill, Commune, Contagion, Control Winds, Geas, Negative Energy Flood, Scrying

6th level (2 slots) Circle of Death, Disintegrate, Eyebite, Harm, Heal, Mass Suggestion, Mental Prison

7th level (2 slots) Finger of Death, Resurrection, Teleport, Whirlwind

8th level (1 slot) Dark Star, Glibness, Maddening Darkness, Telepathy

9th level (1 slot) Astral Projection, Ravenous Void

Innate Spellcasting. Be’lakor has innate magical might. His spellcasting ability is Charisma (spell save DC 27, +19 to hit with spell attacks). Be’lakor can innately cast the following spells:

At Will: Darkness, Misty Step, Minor Illusion, Mending, Darkvision

Multiattack. Be’lakor uses a shadow ability then makes ten attacks: six with his Blade of Shadows, two with his fell claw, and two with betraying shades.

Blade of Shadows. Magic Melee Weapon Attack: +21 to hit, reach 10ft., one target. Hit: 8d6+12 Slashing plus 3d10 Necrotic damage.

Fell Claw. Melee Weapon Attack: +18 to hit, reach 5ft., one target. Hit: 4d8+9 Slashing damage.

Spearing Tail. Melee Weapon Attack: +18 to hit, reach 20ft., one target. Hit: 4d10+9 Piercing damage.

Betraying Shades. Ranged Spell Attack: +19 to hit, range 90ft., one target. Hit: The target rolls for damage with whatever melee weapon it’s holding as its shadow attacks it.

Shadow Ability. Be'lakor uses one of the following Shadow Abilities:

• Penumbral Curse. One creature of Be’lakor’s choice becomes cursed until the start of Be’lakor’s next turn. While that creature is cursed, any bright light appears as dim light to it and any dim light appears as darkness.
• Wreathed in Shades. Until the start of Be’lakor’s next turn, any bright light within 60 feet of him becomes dim light and any dim light becomes darkness. Any area of darkness caused by this is magical darkness that cannot be seen through with normal darkvision.
• Shadow Pact. Until the start of his next turn, Be’lakor gets advantage on saving throws and ability checks that use one of the following abilities: Strength, Dexterity, Constitution, Intelligence.
• Pall of Despair. Be’lakor selects one frightened creature that he can see within 90 feet of him, that creature has disadvantage on saving throws against Be’lakor’s spells and abilities and it cannot perform bonus actions or reactions until the end of Be’lakor’s next turn.

Claw Attack. Be’lakor makes a fell claw attack.

Betraying Shades. Be’lakor makes a betraying shades attack.

Blessing of Shadow. When a creature hits Be’lakor with an attack, Be’lakor can use this reaction to take half damage.

Be’lakor can take 3 legendary actions, choosing from the options below. Only one legendary action option can be used at a time and only at the end of another creature's turn. Be’lakor regains spent legendary actions at the start of his turn.

Detect. Be’laor makes a Wisdom (Perception) check.

Tail Attack. Be’lakor makes a spearing tail attack.

Darkness. Be’lakor casts darkness.Void Sliver. Be’lakor casts mind sliver.

Draught of Terror (Costs 2 Actions). Every creature of Be’lakor’s choosing within 30 feet of him must succeed on a DC 27 Wisdom saving throw or become frightened of him. A creature may repeat this saving throw to end the effect on themselves at the end of each of their turns.