Planar rift device

The planar rift device was an artefact of great power, sealed beneath Athkatla. It would later be found by the bhaalspawn protagonist in Shadows of Amn, and potentially destroyed by a vestige of Amaunator.

History
Very little was known about this artefact. Its creators (perhaps Netherese arcanists) were afraid of its power and sealed it underground, under the guard of an avatar of Amaunator. A small group of followers were guarding it for eternity in a cycle of birth, death and rebirth. As millennia passed though, they began to hate the device and their god, creating a powerful monster, formed of their hatred, in the temple where it was kept (it was possible that the device was partly responsible for this, since it enhanced all negative emotions) that reduced the avatar to a mere shade of its former self. During the Bhaalspawn Crisis, a blind beholder known as the Unseeing Eye found half of the device and plotted to join both halves to achieve its goals. The protagonist could foil his plan, joining the device pieces together to use against him, ensuring the defeat of the otherwise overpowering creature. Later, the device was likely destroyed, and the guardians, freed of their duty, were allowed to die.

Power
As mentioned, little was known of the Planar Rift Device. It was clearly an item of great power, but it seemed linked to evil, since it enhanced negative emotions. It was also hinted that, should it be exposed to the open sky, the result would be catastrophic.