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Gripsoul is a +6 keen longsword, but instead of dealing additional damage on a critical hit, the weapon imprisons the victim in a gem set in the pommel of the sword as per a binding spell heightened to 16th level (DC 30). The same is true of any blow that would otherwise kill a foe or knock him or her unconscious. Only one creature can be so held, but the wielder can release the bound soul at any time with a command word.