Visitor

The Visitor is a phenomenon witnessed by the Crownseekers and Rethamir Volantis during the Hand Conjunction of 1081 SKR. It appeared as a tiny black speck eclipsing Hadar, but, when Misi produced the mysterious black cube she'd found in a meteor impact crater some time before, the cube turned to a sphere, lifted into the air, and began pulsing with evocation magic. This appears to have "called" to the Visitor, which now seems to be headed towards Tol.
It appears to be about the size of a small moon, smaller than either Davron or Kassyle. At its current speed, it will likely arrive close to Tol in the autumn of 1102 SKR. It was given the name the Visitor by Rethamir. When asked to predict the path of the Visitor, the Crown of Heaven showed the Visitor flying directly at Tol and, when asked to predict past 1102 SKR, the system would simply shut down.
In an epilogue, it was revealed that both Lanamara Edanos and Acererak were aware of the likelihood of the Visitor's appearance. Acererak referred to it as "the World Born Dead" and predicted it would mean bad times ahead of the living, but not the undead. He also noted the Visitor was prophecised by Vecna in the Book of Vile Darkness and by Kyuss in De Vermis Mysteriis.