Avatar of Abhorrence (Human Form)

Melded Presence. The avatar is two beings melded into one. It may shift between its human form and its aberrant form at the beginning of each of its turns (no action) or as a legendary action. When it does so, its features and abilities change, but any damage it has taken is transferred.

Unusual Nature. The avatar doesn’t require air, food, drink, or sleep.

Fleet Footed. The avatar can move along vertical surfaces and across liquids on its turn without falling while it moves. Additionally, when the avatar makes a melee attack against a creature, it doesn't provoke opportunity attacks from that creature for the rest of the turn, whether it hit or not.

Call of Carceri. If a creature is killed by the avatar its soul is transported to Carceri at the end of the avatar's next turn unless the soul is resurrected or prevented from leaving the plane.

Ki-Training . The avatar is a 20-th level monk. It has the following ki abilities:

Stillness of Mind (At Will). The avatar ends one effect on itself that causes it to become Charmed or Frightened.

Step of the Wind (5/day).  The avatar gains the effects of the Dash or Disengage action until the end of its turn. For the duration, its jump distance is doubled.

Quickened Healing (4/day). The avatar regains 2d10+10 hit points.

Stunning Strike (3/day). Melee Weapon Attack: +12 to hit, reach 10 ft., 1 target. Hit:  10 (2d8+4) necrotic damage. On a hit, the target has to make a DC 17 Constitution saving throw or be stunned until the end of the avatar's next turn. On a successful save, the target’s Speed is halved until the start of the avatar's next turn, and the next attack roll made against the target before then has Advantage.

Flurry of Blows (2/day). The avatar makes three additional Unarmed Strikes.

Multiattack. The avatar makes four attacks with its unarmed strikes. Any number of which can be replaced by an ability from the Ki-Training feature. It then uses two of its Boons of Carceri features.

Unarmed Strike. Melee Weapon Attack: +12 to hit, reach 10 ft., 1 target. Hit:  10 (2d6+4) necrotic damage. 

Boons of Carceri:

Grasping Chains. Melee Weapon Attack: +12 to hit, reach 10 ft., 1 target. Hit: 6 (1d6+3) necrotic damage. A creature hit by this attack has to make a DC 20 Strength Saving throw or become restrained for the next minute as chains of tar erupt around it. The creature may reroll its saving throw at the end of each of its turns or another creature may use its action to attempt to break free a restrained creature, competing against the Grasping Chains save DC.

Constrict. The avatar tightens the chains around a creature that it can see and that is restrained by its Grasping Chains ability. The creature then immediately takes 10 bludgeoning damage and an additional 5 at the start of each of its turns, for as long as it is restrained by the chains. The effects of Constrict stack. 

Crawl. If the avatar has at least one creature restrained by its Grasping Chains ability, it may cause some of those chains to crawl up to 15 ft in any direction and attempt to restrain a creature as per the Grasping Chains ability. Using this ability lowers the DC of the save by 2 for each additional restrained creature.

Leech. The avatar attempts to sap the life force out of 1d4 creature restrained by its Grasping Chains ability. The creature(s) have to make a DC 20 Constitution saving throw or be unable to regain hit points until the start of the avatar's next turn.

Choke (Recharge 4-6). The avatar attempts to choke a creature restrained by its Grasping Chains ability. The creature is lifted up to 20 ft off of the ground (losing any Constrict stacks) and has to make a DC 20 Constitution saving throw, taking 35 (8d8+15) bludgeoning damage and beginning to suffocate on a fail, or taking half damage and not suffocating on a success. A creature ceases suffocating if it regains the hit points it lost to this ability or if it doesn't need to breathe. 

Deflect Energy. When the avatar is hit by an attack it may use its reaction to attempt to reflect it. When it does so, the damage it takes from the attack is reduced by 2d10 +14. If this reduces the damage to 0 the avatar may choose a creature it can see within 5 feet of itself if the attack was a melee attack or a creature it can see within 60 feet of itself that isn’t behind Total Cover if the attack was a ranged attack. That creature must succeed on a Dexterity saving throw or take 20 (4d8 +7) damage. The damage is the same type dealt by the attack.

Evasion. When the avatar is subjected to an effect that allows it to make a DEX saving throw to take only half damage, it may use its reaction to instead take no damage if it succeeds on the saving throw, and only half damage if it fails.

The avatar has a pool of three legendary actions that are shared by its aberrant and its human form.

Flowing Movements (1 Action). The avatar moves up to its speed without provoking opportunity attacks.

Command of Carceri (2 Actions). The avatar uses one of its Boons of Carceri abilities.

Shift (2 Actions). The avatar shifts into its aberrant form.