Godsbane

In The Avatar Series, a quintet of novels based in the Forgotten Realms setting, Godsbane was a magical sword which was actually a manifestation of the deity Mask and was wielded by the then-mortal Cyric during the Time of Troubles. Cyric acquired the sword by murdering a halfling named Sneakabout, who in turn killed the former wielder of the sword.

Cyric named the sword "Godsbane" because while he was a mortal, he used it to slay Bhaal (then Lord of Murder), and after becoming a deity, he used it to kill Leira, Lady of Deception.

Godsbane needs to consume the energy of souls to survive. "She" sucks all the blood from her victims, giving her a blood-red hue. When starved for a long time, she gradually fades to white. Before she came into the grasp of Cyric, Godsbane had driven all of her previous wielders mad, forcing them to sustain her by killing victims. Eventually, the blade would be stolen by another, and the former wielder's thoughts would always be focused on recovering it. He/she would never sleep until recovering the blade or die trying.

This was also the sword Cyric used to kill Kelemvor Lyonsbane while atop Blackstaff Tower. To spite Cyric for trying to break her will while he was a mortal, Godsbane hid Kelemvor's soul from him. During a revolt in the City of Strife that marked the end of Cyric's reign as Lord of the Dead, Cyric learned of this and snapped the blade in two. This revealed the sword to be an aspect of Mask, the god of thievery and intrigue. By doing this, Cyric greatly weakened Mask and gained the portfolio of intrigue, along with shadowy characterics. Eventually, Mask regained his portfolio of intriuge, much to the disdain of Cyric.