Eye of the druuthbane

An eye of the druuthbane was a magical item designed to expose and thwart a druuth—a band of doppelgangers in the service of a mind flayer.

Description
It was a yellow crystal about as big as a human fist. It weighed.

Powers
An eye of the druuthbane had a variety of powers dedicating to foiling the powers of doppelgangers and illithids. First, if a doppelganger was within, it glowed red; if an illithid was within , it glowed blue; and if both were , it glowed violet.

Second, when grasped in one's hand, it bolstered the bearer's mental defenses and force of will.

Third, it could be used once a day to fire a red beam at a creature that, if it was a doppelganger, would be forced to return to its true form for up to half a minute if it couldn't resist.

History
The first eye of the druuthbane was fashioned by a wizard who battled a powerful druuth. It was once exclusively associated with Waterdeep.

After that time, it was copied and spread far and wide to oppose other druuth.

Creation
Creating an eye of the druuthbane required the spells resistance, detect thoughts, and polymorph other. One was valued at 18,000 gp.