The Orb of Oblivion is a magical device able to contain numberless souls in it. The souls also can be transported to any dead body using black arts.
Crafted by the southern people's most gifted craftsmen it was used during the Necromancer war, as Jandor used it on the Staff of Oblivion to defeat Necromancers and store their souls in it, making them ultimately powerless. After the war, Jandor gave it to Horvath who, in attempt to hide it forever, transported the Orb to the Earth where it was found by Jack, unacquainted with its powers.
Years later, Hecubah successfully attempted to transport the Orb back to the Land of Nox by conjuring a portal between the two worlds. However, Jack was also transported along with the Orb, although they landed in quite distant places.
After assembling Halberd with the Heart Of Nox and the Weirdling, Jack entered Hecubah's fortress and finally reached the Orb and assembled the Staff of Oblivion. He then used it to either kill, or clean Hecubah of her necromancy.