Xander's disc

This object appeared in the episode: The Replacement

and was carried by the Xander Double who appeared to be the stronger willed of the two. The weaker willed double feared it was a magical device used to disorient or hypnotize because, while the stronger willed Xander carried it he was able to prolong his employment and rent an appartment and convince the rest of the "Scoobies" that he was indeed the REAL Xander.

In the end it is revealed that the disk was nothing more than a nickle that had been flattened on a rail-road track and that the stronger willed Xander had found on the work site and thought it was cool.