Claw (2/turn). Melee Weapon Attack: +10 to hit, reach 1 m. Hit: 12 (2d6 + 5) slashing damage plus 21 (6d6) necrotic damage.
Imprison Soul (1/turn). The devourer chooses a living humanoid with 0 health that it can see within 5 meters of it. That creature is teleported inside the devourer’s ribcage and imprisoned there. A creature imprisoned in this manner has disadvantage on death saving throws. If it dies while imprisoned, the devourer regains 25 health, immediately recharges Soul Rend, and gains an additional action on its next turn. Additionally, at the start of its next turn, the devourer regurgitates the slain creature as an action, and the creature becomes an undead. If the victim had 2 or fewer Health Dice, it becomes a zombie. If it had 3 to 5 Health Dice, it becomes a ghoul. Otherwise, it becomes a wight. A devourer can imprison only one creature at a time.
Soul Rend (Recharge 6). The devourer creates a vortex of life-draining energy in a 5-meter radius centered on itself. Each humanoid in that area must make a Difficulty 18 Fortitude saving throw, taking 44 (8d10) necrotic damage on a failed save, or half as much damage on a successful one. Increase the damage by 10 for each living humanoid with 0 health in that area.
No concoctions, maneuvers, or spells
All creatures in this system should have maneuvers or spells. You should add some maneuvers or spells to this creature. If you do so, please make a suggestion on github so I can finish adding maneuvers and spells to all creatures via https://github.com/mlenser/kryx-rpg-issues/issues/9.