"He looked at the small stone in his hand. If Hakann's information was correct, the stone was able to spread darkness over a wide area when exposed to force of any kind. It was not what Kavala had expected, nor was he entirely satisfied with it... but he would use it to the best of his abilities in order to acquire more secrets of the Vault."
The Shadowstone is an ellipse stone found in The Vault, which can be used to engulf an area in total darkness. It was given by Hakann to Kavala.
The stone is a smooth metallic ellipse, featureless and small enough to be held in one's hand. When met with any force, including physical impact, the ellipse releases an explosion of shadow, engulfing up to fifteen meters in total darkness.
The Shadowstone was found among the contents of The Vault by the Piraka. Hakann gave the stone to Kavala as a token of alliance and told him to use it to kill his enemies and bring their remains to Hakann. Kavala took the stone and left for Onu-Koro.
Kavala successfully used the stone to confuse and kidnap Kirgan. However, later on, he was knocked out by Lash in an Onu-Koro bar and the stone was taken from him by Toa Vesun. With help from Khervos, Vesun discovered the power of the stone, after which Lash began to demand it for herself. The stone was confiscated by the Ussalry as evidence against Kavala.
"Suddenly there was a clang from somewhere nearby, and everything went black in an instant."