The Abaddon Stone.

The Abaddon Stone... a large, seventy-carat, blood-red Garnet said, in ancient legend, to have been mounted in the sword pommel of an unspeakably evil Entity who was called by name: "Baelar... Lord of The Underdark," and whispered to be a conduit to his malignant will to unleash his "Night of Shadows Rising," which will turn all back to Chaos, as it was in the beginnings of time itself.