Hand of Vecna
The Hand of Vecna was one of two magical artifacts connected to the malevolent lich turned demigod turned deity known as Vecna (the other being the Eye of Vecna). The Hand is Vecna's actual left hand, and is possessed of many magical powers. The Hand may only be used if it replaces the left hand of its user.
It grants enhanced strength, resistance to the magic missile spell, the ability to rot plants and cause instant death, and other untold powers. However, it also has a curse- anyone who wields it is eventually subject to artifact domination. Once dominated, they are compelled to gain magical power, forge an empire, destroy the Sword of Kas, and summon Vecna back to Oerth.