Corpse Marshal

Pain of the Dead. The corpse marshal feels no pain, allowing it to continue the fight, even after imminent death. If damage reduces the harbinger to 0 hit points, it must make a Constitution saving throw with a DC of 5 + the damage taken, unless the damage is radiant or from a critical hit. On a success, the marshal drops to 1 hit point instead and can use its reaction to make a melee attack.

Watch My Back. The corpse marshal has advantage on Wisdom (Perception) checks made that rely on sight. Additionally, the corpse marshal cannot be surprised.

Innate Spellcasting. The corpse marshal's innate spellcasting ability is Wisdom. It can innately cast the following spells, requiring no material components:

At will: misty step

3/day each: blur

Multiattack. The corpse marshal makes three melee attacks, only one of which can be its soul drain.

Lance. Melee Weapon Attack: +9 to hit, reach 10 ft., one target. Hit: 24 (3d12 + 5) piercing damage. This attack is at disadvantage against targets within 5 feet.

Necrotic Dagger. Melee Weapon Attack: +8 to hit, reach 5 ft., one target. Hit: 13 (2d8 + 4) piercing damage plus 7 (2d6) necrotic damage.

Soul Drain. Melee Weapon Attack: +9 to hit, reach 5 ft., one target. Hit: 21 (3d10 + 5) necrotic damage. The target must succeed on a DC 16 Constitution saving throw or its hit point maximum is reduced by an amount equal to the damage taken. This reduction lasts until the creature finishes a long rest. The target dies if this effect reduces its hit point maximum to 0. If the target has taken necrotic damage this turn, this saving throw is made at disadvantage.