Amalthea's Soul Reaver

Summon a spectral scythe in your hands if you are not wielding anything else. Attacks with this scythe use the spell attack modifier and deal 4d6 necrotic damage. If this attack kills the target, they must make a Constitution saving throw. On a failed save, their soul is locked in the Fugue Plane and they cannot be turned undead or resurrected by any means for a week.

At Higher Levels. When you cast this spell using a spell slot of 6rd level or higher, you can increase the duration of the prevention by a month (6th), a year (7th), or two years (8th). If this spell is cast at 9th level, the effect is permanent.