Abyssal Sentinel

Sentinel Shell 3/Day. The abyssal sentinel coats itself in darkened energy from its abyssal plate armor, raising its ac by 2 until the start of its next turn. A charge from this ability can also be used to add a +2 to a saving throw that the sentinel would otherwise fail.

Peerless Swordsmanship. If the abyssal sentinels blade is dispelled it can make a shadow slash attack as a bonus action. 

Forged in Shadows. If the abyssal sentinel is subjected to necrotic damage it instead heals an amount of hit points equal to the amount of damage taken and can add an extra 9 (2d8) necrotic damage onto its next shadow slash attack.

Sunlight Sensitivity. While in sunlight, the sentinel has disadvantage on attack rolls, as well as on Wisdom (Perception) checks that rely on sight.

Shadow Slash. Melee Weapon Attack: +11 to hit, reach 10 ft., one target. Hit: 17 (2d10 + 6) slashing damage and 17 (3d10) necrotic damage. This attack can destroy the beacon of hope (dispelling it entirely if one creature with it on them is hit but not targeted by the damage of this attack) and daylight spells if they are targeted specifically.

Black Blade Beam. Ranged Weapon Attack: +11 to hit, reach 30 ft., one target. Hit: 22 (3d10 + 6) necrotic damage. The sentinel sends a beam of dark energy out from its blade targeting a creature within range. If this attack strikes the daylight spell it is immediately dispelled.

Dancing Blade of the Black Sentinel 1/Day. The abyssal sentinel summons a dark blade that dances around it within 30 feet. This blade has a +11 to hit and deals 44 (8d10) necrotic damage. The blade can be moved up to 20 ft. and used to attack as a bonus action on the sentinels turns but can never be further than 120 ft. away from it. A creature hit by this weapon cannot regain hit points until the start of its next turn.
This blade, once summoned, counts as a 5th level spell that the sentinel is not concentrating on. It can be dispelled by the dispel magic or similar magics.

Dancing Blade. The abyssal sentinel moves its dancing blade up to 20 ft. and makes an attack with it.

Darkness Grasp. When a creature moves out of the shadow sentinel's melee range it attempts to hold them in place through the forces of its dark magic. They must roll a DC 16 Constitution saving throw. On a failure their movement speed is reduced to 0 and they take 10 (3d6) necrotic damage.