Multiattack. Three Devourer's Cleaver or Necrotic Bolt attacks. It can replace one attack with Life Drain attack.

Devourer's Cleaver. Melee Weapon Attack: +7 to hit, 5 ft., one target, 10 (2d6+3) slashing damage + 9 (2d8) necrotic.

Life Drain. Melee Spell Attack: +8 to hit, 5 ft., one creature,. 17 (3d8+4) necrotic. Target's hp max is reduced by amount equal to damage taken (DC 16 Con negates hp max). Reduction lasts until target finishes a long rest. Target dies if this reduces its hp max to 0.

Necrotic Bolt. Ranged Spell Attack: +8 to hit, 120 ft., one target, 17 (3d8+4) necrotic.

Invisibility. Magically turns invisible (with items worn/carried) until it attacks uses Grasping Claws or concentration ends (as a spell).

Grasping Claws (Recharge 5-6). Calls dozens of ghostly skeletal claws to erupt from a point on the ground it can see within 60' of it. All within 15 ft. of that point: 31 (7d8) necrotic and restrained 1 min (DC 16 Dex half damage not restrained). Restrained creature can re-save at end of each of its turns success ends effect on itself.