Spectral Shielding.
The Sentinel can project a shield of energy around itself or an ally within 10 feet, granting +2 AC to the target until the start of its next turn.

Haunting Presence.
Any creature that starts its turn within 10 feet of the Sentinel must make a DC 13 Wisdom saving throw or have disadvantage on its next attack roll.

Ethereal Step.                                                                                                                                  The Spectral Sentinel can move through other creatures and objects as if they were difficult terrain.

Ethereal Strike.
Melee Weapon Attack: +5 to hit, reach 5 ft., one target.
Hit: 15 (2d10 + 3) force damage.

Spectral Lunge (Recharge 5-6).
The Sentinel rushes forward in a straight line up to 30 feet, passing through creatures. Each creature in its path must make a DC 13 Dexterity saving throw or take 20 (4d8) necrotic damage.