The Grave Binder

Grave Binder is an enchanted dagger +2. It can be obtained if the partner of the assassin Slythe is killed in the last chapter of the game in the Undercellar.

In-game description
"Dagger +2, longtooth: 'Grave Binder.' Discovered relatively recently by adventurers in the south, the abilities of this weapon went unknown for several years. Magic tomes eventually revealed its extensive history as an assassin's tool and it was dubbed the Grave Binder. It was stolen soon after."