Never Sated. If the Abysswalker is killed by a creature before completeling its mission, when being remade, the Abysswalker gaind +1 bonus AC, hit die, saving throws, attack and damage rolls. This effect stacks until he tasted victory

Autosarcophagy. The Abyss is always hungry. If the Abysswalker cannot land a weapon attack, it consumes a part of himself taking 6 (2d6) damage at the start of its turn. Their weapon attacks gain and additional +1 for each time the Abysswalker misses. The turn after it ends, the bonus dissapears and has to be restarted. 

Never-ending Stalk. The Abysswalker will have advatage on Wisdom (Survival) checks while its prey is in an Abyssal zone.

Vigor Drain. Any attempt to heal while within 10 ft the Abyswalker will result in pain. The healing dice must be rolled twice, the second number being the amount of psychic damage the target takes. 

Magic Weapons. The Abysswalkers weapon attacks are magical. 

Magic Resistance. The Abysswalker has advantage on saving throws agains spells and other magical effects.

Sisyphean Existence. As long as its goal isnt fulfilled, the Abysswalker is tasked with roaming the material plane to complete its goal. When killed he will rejuvinate once every 1d6 days. 

Multiattack The Abysswalker makes 2 melee attacks

Slice Attack. Melee Weapon Attack: +7 to hit, reach 5 ft., one target. Hit: 14 (2d8 + 5) slashing damage. 

Stab Melee Attack. Melee Weapon Attack: +7 to hit, reach 5 ft., one target. Hit: 14 (2d8 + 5) piercing damage. 

Swat Melee Attack. Melee Weapon Attack: +7 to hit, reach 5 ft., one target. Hit: 10 (1d10 + 5) bludgeoning damage. Target must succeed a DC 12 Strenght saving throw or be knocked prone.

 Impending Death (Recharge 18–20). The Abysswalker pulses with death as he surrounds a 30 ft. area around him. Each creature in that area must make a DC 14 Dexterity saving throw, taking 20 (5d8) psychic damage on a failed save, or half as much damage on a successful one.