Special Trait Name. Psychic reflection barrier.

Any attack or spell, instead of targeting the abysswalker will target the source. If the attack features a saving throw, the attacker will have to save against their own attack.

Innate Spellcasting. The abysswalker's spellcasting ability is charisma (spell save DC 17, +5 to hit with spell attacks). The abysswalker can innately cast the following spells, requiring no material components:
At will: Detect thoughts, silent image 
3/day each: Fear, Confusion, Charm person

Multiattack. The abysswalker can attack twice with it's Arm slam attack or once with it's bite.

Phase walk. The abysswalker can enter this form as an action, in this form the abysswalker has 20 feet of flying speed and can pass through physical objects with this movement, if it ends it's turn inside an object, the abysswalker cannot breathe, while in this form any attacks that target the abysswalker miss and any of the abyss walker's attacks miss, the abysswalker appears as a lightly translucent shadow in this state, the abysswalker can end this effect on itself as a bonus action.

Arm slam. Melee Attack: +14 to hit, reach 10 ft., one target. Hit: 30 (6d6 + 10) bludgeoning damage.

Bite. Melee Weapon Attack: +14 to hit, reach 5 ft., one target. Hit: 11 (3d6 + 5) piercing damage. If the target is a Medium or smaller creature, it must succeed on a DC 15 Dexterity saving throw or be swallowed by the abysswalker. A swallowed creature is blinded and restrained, if it has a creature currently swallowed, the abysswalker can target only the creature it has swallowed with this attack, causing it to take 21 (2d6) piercing damage, it has 3/4 cover against attacks and other effects outside the abysswalker, If the abysswalker takes 30 damage or more on a single turn from a creature inside it, the abysswalker must succeed on a DC 21 Constitution saving throw at the end of that turn or regurgitate the swallowed creature, which fall prone in a space within 10 feet of the abysswalker. If the abysswalker dies, a swallowed creature is no longer restrained by it and falls prone in a space within 10 feet of the abysswalker.

Amnesia infliction. The abysswalker can inflict a target with amnesia, the target must succeed a DC 15 intelligence save or forget the abysswalker exists entirely. On a successful save the target remembers the encounter with the abysswalker, on the next dawn the target must make another intelligence save with the DC increased by two (15, 17, 19, 21 etc etc) the target must continue to make these saves until they fail or otherwise forget the abysswalker exists.