D: Sigil

First, you must prepare an empty clay jar with a Sigil. By the casting of this spell you traps within the prepared jar a disembodied soul of [dice] HD or less. Souls on their way to the underworld or other final reward may be captured automatically, but free-willed souls such as incorporeal undead are permitted a saving throw. A soul may be freed in exchange for a favor, traded as sorcerous currency, or consumed for temporary power, such as a [dice] bonus to a single roll or [sum] temporary hit points.

soul + harvest

adapted from Wonder & Wickedness