The Righteous Hand of Ser Goiter

A member of the Righteous Brotherhood, Ser Goiter lost his arm to an infected toddler bite soon after the Siege of the Black Orphanage. Consulting the order's blacksmiths, he had them build a prosthetic flexible enough to weld a pen, or a mace. Later, he had it blessed by the Most Righteous Poomba, giving the wearer the bonus of +2 (Blessed) Damage to all magical creatures, undead and orphans.

Of course, you have to lose your arm first.

via Retronaut