Abbadon

Innate Spellcasting. Abbadon's spellcasting ability is Charisma (spell save DC 19, +11 to hit with spell attacks). Abbadon can innately cast the following spells, requiring no material components:

At Will: Eldritch Blast (4 beams), Infestation (4d6)

1/Day Each: Blight, Counterspell, Darkness, Dominate Monster, Hellish Rebuke, Hold Monster, Mirror Image, Mental Prison, Plane Shift

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

Pride's Pursuit (1/Turn). When Abbadon misses a target with a weapon attacks, he can immediately make another weapon attack against it.

Scourge (Recharge 5-6). When Abbadon hits a creature with a melee weapon attack, he can afflict it with a lingering, insidious wound. The target must succeed a DC 19 Constitution saving throw. On a failed save, the target loses 1d10 hit points at the start of each of its turns for 1 minute. This effect ends if the target is subjected to magical healing, or if it or another creature passes a DC 19 Wisdom (Medicine) check to treat the wound. 

Shadow Sight. Magical darkness does not impede Abbadon's darkvision.

Bonds of Torment (Recharge 5-6). Abbadon conjures magical spiked chains that lash out at a creature he can see within 30 feet of him. The target must make a DC 19 Dexterity saving throw. On a failure, the target takes 24 (8d6) piercing damage and is restrained. While restrained in this way, the target cannot teleport or use interplanar travel, and it takes 9 (3d6) piercing damage at the start of each of its turns. On a successful save, the target takes half damage and is not restrained.

As an action on its turn, the restrained target can make a DC 19 Strength (Athletics) check or Dexterity (Acrobatics) check. On a success, the target escapes and the chains disappear.

Multiattack. Abbadon makes two Profane Blade attacks.

Nefarious Cyst (1/Day). Abbadon channels dark magic into his hand and touches a creature he can see within 10 feet of him. The target must make a DC 19 Constitution saving throw. On a failed save, the target takes 32 (8d8) necrotic damage, and a horrid cyst forms on their body where Abbadon touched them. The affected creature has disadvantage on saving throws against Abbadon and effects caused by him. On a successful save, the creature takes half damage and suffers no other effects.

Any magic that removes disease can cure the cyst. Alternatively, the cyst can be removed with a successful DC 19 Wisdom (Medicine) check. Nefarious Cyst has no effect on incorporeal creatures and creatures that are immune to disease.

Profane Blade. Melee Weapon Attack: +11 to hit, reach 10 ft., 1 target. Hit: 16 (2d10 + 6) slashing damage plus 5 (1d10) necrotic damage.

Pernicious Spike (Recharge 5-6). Melee or Ranged Spell Attack: +11 to hit, reach 10 ft. or range 30 ft., one target. Hit: 6 (2d6) poison damage, and the target must succeed on a DC 19 Constitution saving throw or be poisoned for 1 minute. A target can repeat the saving throw at the end of each of its turns, ending the effect on itself on a success.

Word of Woe (1/Day). Abbadon casts Bane as a bonus action, using Charisma as his spellcasting ability.

Abbadon 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. Abbadon regains spent legendary actions at the start of his turn.

Cantrip. Abbadon casts Eldritch Blast or Infestation.

Profane Blade. Abbadon makes a Profane Blade attack.

Bonds of Torment (3 actions). Abbadon recharges and uses Bonds of Torment.