Device used to capture rising or falling souls, the first ingredient in manufacturing zarogoths.
The Dungeon Anarchist's Cookbook entry on the Zarogoth spells out how they're made: souls are captured with a soul crystal as they rise or fall, the energy is rerouted through a corruption spell, and the mixture becomes an oil-like soup poured into a humanoid sausage casing.
The process leaves nothing of the person behind — the resulting creatures retain no personality of the fallen. They just come out sadistic.
The soul-harvesting component behind the enemy's mass-produced ground troops.
Also appears in books you've already read — spoiler-safe to their endings: