Demon stone

A demon stone was a magical tool used in the binding and summoning of extraplanar outsiders.

Description
A demon stone was a large cut crystal or gemstone, approximately 1 foot (30.5 centimeters) long and 3 inches (7.6 centimeters) in diameter. When being used as part of a spell or ritual, a demon stone would glow prismatically.

Powers
While the full extent and utility of a demon stone is unclear, they were broadly useful in the binding and summoning of powerful beings from outside the Prime Material plane.

A demon stone was capable of imprisoning even extraordinarily powerful extraplanar creatures, but only under strict conditions. At least two such beings had to be trapped simultaneously, and these beings had to be hostile toward each other. The essences of these outsiders would then be trapped inside the demon stone in an endless battle while skeletal placeholders of their physical bodies remained in stasis outside with the demon stone hovering above them. The stone could then be warded or protected to keep the outsiders trapped. However, powerful outsiders were still able to reach out and manipulate mortals while imprisoned.

History
At some point in the mid-to-late 13 century DR, a demon stone was used by Khelben "Blackstaff" Arunsun to trap the githyanki general Cireka and the slaad lord Ygorl when the two's extraplanar armies clashed in the Rawlinswood and threatened to overrun all of Faerûn. The two were trapped inside the stone, with their bodies safely hidden behind magical barriers within the Gemspark Mine in Damara, for nearly a century. They were freed thanks to the machinations of Ygorl, who managed to reach out from the prison and lure three adventurers—Illius, Rannek, and Zhai—to the mines and trick them into breaking the wards around the demon stone.

In the mid-to-late 14 century DR, a yuan-ti temple to Merrshaulk in Chult incorporated a demon stone into their ritual sacrifices. They used it to open a portal through which a demonic aspect of their god could enter the Prime Material plane and gorge himself on living sacrifices. This demon stone was taken from the temple by Illius, Rannek, and Zhai, who sought to use it to once again trap Cireka and Ygorl. However, Ygorl succeeded in killing Cireka before the two could be imprisoned again, thus rendering the demon stone useless to the three heroes and forcing them to fight the slaad lord directly.

Notable Owners of Demon Stones

 * Illius of Silverymoon
 * Khelben Arunsun

Appearances

 * Video games
 * Forgotten Realms: Demon Stone