Shadow Stealth. While in dim light or darkness, the cairn shadowraith can take the Hide action as a bonus action.

Stone Camouflage. The cairn has advantage on Dexterity (Stealth) checks made to hide in rocky terrain

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

Umbral Armor. If the cairn shadowraith is in dim light or darkness, its AC can't be less than 14 plus its Dexterity modifier, regardless of what kind of armor it is wearing

Unearthly Movement. The cairn shadowraith ignores difficult terrain formed from nonmagical earth, sand or rock. It moves across mud or quicksand as if it were solid ground and can move through a space as narrow as 1 inch wide without squeezing.​

Multiattack. The cairn shadowraith makes two death fist attacks or two phantom boulder attacks. It can use its Doom Strike in place of one attack.

Death Fist. Melee Weapon Attack: +8 to hit, reach 15 ft., one creature. Hit: 12 (2d8 + 3) bludgeoning damage plus 18 (4d8) necrotic damage. The target must succeed on a DC 18 Constitution saving throw or its hit point maximum is reduced by an amount equal to the necrotic damage taken. This reduction lasts until the target finishes a long rest. The target dies if this effect reduces its hit point maximum to 0.

 Phantom Boulder. Ranged Weapon Attack: +8 to hit, range 60/240 ft., one creature. Hit: 14 (2d10 + 3) psychic damage plus 14 (4d6) necrotic damage. The target must succeed on a DC 18 Constitution saving throw or its hit point maximum is reduced by an amount equal to the necrotic damage taken. This reduction lasts until the target finishes a long rest. The target dies if this effect reduces its hit point maximum to 0.

Soul Grip. Melee or Ranged Weapon Attack: +8 to hit (automatically hits a restrained opponent), reach 15 ft. or range 15/60, one target. Hit: 25 (4d8 + 7) psychic damage plus 27 (6d8) necrotic damage and the target is grappled (escape DC 18) and the target is grappled (escape DC 18). Until this grapple ends, the target is restrained, and the cairn shadowraith can't use Soul Grip or Doom Strike on another target. The target must succeed on a DC 18 Constitution saving throw or its hit point maximum is reduced by an amount equal to the necrotic damage taken. This reduction lasts until the target finishes a long rest. The target dies if this effect reduces its hit point maximum to 0.
 In addition, if the target is a creature, it suffers 1 level of exhaustion if it fails the saving throw. If the target fails the saving throw by 5 points or more, it suffers an additional level of exhaustion. This exhaustion remains until it is healed magically: a lesser restoration can remove one level of exhaustion from a victim with two or fewer levels, a greater restoration will remove three levels of exhaustion. The target dies if it suffers 6 levels or exhaustion.

VARIANT: SPECTRAL GRASP
Many cairn shadowraiths have the following trait.
 Spiritual Grapple. The cairn shadowraith's Soul Grip seizes hold of a target's spirit and lifeforce rather than its corporeal body. A creature that is spiritually grappled can use its action to try to escape. To do so, it must succeed on a Charisma or Wisdom saving throw against the escape DC of the grapple.

Create Specter. The cairn shadowraith targets a humanoid or giant within 30 feet of it that has been dead for no longer than 1 minute and died violently. The target's spirit rises as a specter in the space of its corpse or in the nearest unoccupied space. The specter is under the cairn shadowraith's control. The cairn shadowraith can have no more than thirteen specters under its control at one time.

Sacrifice Specter. If the cairn shadowraith is hit by an attack or fails a saving throw, it can sacrifice a specter under its control within 30 feet of the cairn wraith. The specter is destroyed, but the attack misses the cairn wraith or its saving throw succeeds.​

Rock Catching. If a rock or similar object is hurled at the cairn shadowraith, it can, with a successful DC 10 Dexterity saving throw, catch the missile and take no bludgeoning damage from it.