Corum wielding Traitor and the Runestaff
During the events of The Sword and the Stallion, the final book of the second Corum trilogy, a magic sword is forged for Prince Corum which, besides being mooncolored, shares many characteristics with the Black Swords wielded by other Eternal Champions. And, like Stormbringer, it ultimately slays its wielder at the end of the book. However, Corum is later revived, and continues to wield Traitor in The Quest for Tanelorn Books 2-3 and Elric: The Balance Lost.
While not explicitly stated, Traitor is most likely a manifestation of the Black blade, as Corum was having visions of other champions, consorts, companions and black blades during its creation, as it's been confirmed that the black blade does not always manifest in the color black.