Abyssal Weapons. Abyss's weapon attacks are magical. When Abyss hits with any weapon, the weapon deals an extra 6d8 necrotic damage (included in the attack).

Divine Awareness. Abyss knows if it hears a lie.

Touch of Pure Evil. Necrotic damage dealt by Abyss ignores resistance and immunity.

Innate Spellcasting. Abyss's spellcasting ability is Charisma (spell save DC 25). It can innately cast the following spells, requiring no material components:

At will: Detect good and evil, invisibility/self, contact other plane/no int save, telepathy, shape change

5/day each: Circle of death, Finger of death, Resurrection, Modify Memory, dominate monster

1/day each: power word kill, meteor swarm

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

Multiattack. Abyss makes 4 glaive attacks and or 2 glaive attacks and a Slaying Bolt. 

Edge of Corruption. Glaive, Melee Weapon Attack: +18 to hit, reach 5 ft., one target. Hit: 22 (4d10 + 8) slashing damage plus 27 (6d8) necrotic damage.

Slaying Bolt. Ranged Weapon Attack: +16 to hit, range 600 ft., one target. Hit: 15 (2d8 + 6) piercing damage plus 27 (6d8) necrotic damage. If the target is a creature that has 100 hit points or fewer, it must succeed on a DC 18 Constitution saving throw or die.

Flying Glaive. Abyss releases its glaive to hover magically in an unoccupied space within 5 feet of it. If Abyss can see the sword, Abyss can mentally command it as a bonus action to fly up to 80 feet and either make one attack against a target and return to Abyss's hands. If the hovering glaive is targeted by any effect, Abyss is considered to be holding it. The hovering glaive falls if Abyss dies.

Touch of the Abyss(7/Day). Abyss touches another creature to bestow upon it a manifestation of his dark and corrupted will. Abyss uses an action to make a melee spell attack if the target is unwilling. This magic is ancient and of the gods leaving the few mortals who manage to gleam some information utterly mad. This ability is up to DM discretion and. Could include unique curses against enemies and boons for those who serve willingly.

Consume Essence (At Will). Abyss uses an action to choose a creature he can see within 60ft. Abyss attempts to drain that creatures life force. The target creature must make a constitution saving throw DC 25 or take 10D10 necrotic damage, half on a success. If the target creature is a demon lord who contains a portion of the Shard of Pure Evil that creature has disadvantage on the save. If a Demon Lord fails this save they are stripped of power and rank and reduced to the form and status of maise.

Abysscan take 4 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. Abyss regains spent legendary actions at the start of its turn.

Teleport. Abyss magically teleports, along with any equipment it is wearing or carrying to a location on the same plane of existence. Abyss may take up to 8 other willing creatures

Glaive Attack (Costs 1 Action)

Slaying Bolt (Costs 2 Actions)

Shard Burst (Costs 2 Actions). Abyss emits magical, divine shards of pure evil that manifest as black needles. Each creature of its choice in a 20-foot radius must make a DC 23 Dexterity saving throw, taking 14 (4d6) fire damage plus 14 (4d6) necrotic damage on a failed save, or half as much damage on a successful one.

Corrupted Gaze (Costs 3 Actions). Abyss targets one creature it can see within 30 feet of it. The target must succeed on a DC 22 Constitution saving thow or suffer the corruption of the Abyss flipping it's alignment and causing madness. During the first 24 hours a creature under these effects may be cured using level 5 magic or greater. After 24 hours a wish spell or divine intervention is required.

 Cast a Spell (costs 3 actions) Abyss casts a spell if he has any left.