The Six Faces of Delusion was a headdress dating back to the middle of the Sumaran Era. It had five faces, with the wearer making up the sixth.
Ambril kept it in his museum on Manussa. He believed the legend surrounding the Six Faces of Delusion to be folly as it had only five faces. The Fifth Doctor instructed him to wear it, proving there were six. (TV: Snakedance)