Soul Hunter

Monster Manual Entry: The Soul Hunter
Alignment: Lawful Evil
Danger Rating: S
Health: 300 (20d10 + 180)
Stats:
Strength: 22 (+6) Dexterity: 10 (+0) Constitution: 26 (+8) Intelligence: 14 (+2) Wisdom: 16 (+3) Charisma: 12 (+1) Saving Throws: Constitution +12, Wisdom +9
Skills: Perception +9, Stealth +4
Senses: Darkvision 120 ft., passive Perception 19, Truesight 60 ft.
Armor Class: 20 (natural armor)
Speed: 9 meters (30 feet)
Fighting Style: The Soul Hunter is a patient and relentless adversary. This 3 meter tall ironclad monstrosity tracks down mortals who have escaped from the null realm and strikes when the target is vulnerable and alone. It relies on its potent magical abilities to render itself invisible to all but those with Truesight, ensuring surprise and advantageous positioning in combat.
Active Abilities:
Mark of Doom (Recharge 5-6): The Soul Hunter marks a target with a magical sigil, allowing it to track the target's location unerringly. The mark cannot be dispelled or removed by magical means. Once marked, the Soul Hunter always knows the exact location of the target, even across planar boundaries.
Mortal Veil: As an action, the Soul Hunter activates a potent spell that cloaks itself in an ethereal shroud, rendering it completly unnoticable to any creature without True Divinesight. The effect lasts until the Soul Hunter attacks or takes damage. Creatures afflicted with Mark of Doom can see the Soul Hunter.
Passive Abilities:
Unerring Tracker: The Soul Hunter automatically succeeds on Wisdom (Perception) checks to detect the marked target, regardless of any magical or mundane attempts to hide.
Resilient Soul: The Soul Hunter has advantage on saving throws against spells and other magical effects.
Damage Rolls:
Multiattack: The Soul Hunter makes two attacks with his large executioner's sword.

Executioner's Sword: Melee Weapon Attack: +12 to hit, reach 3 meters, one target. Damage: 5d10 + 10. If target is affected by mark of doom this attack is always critical hit.

Planar Being, Servant of The Horseman of Death.