 At the end of "Beware the Grey Ghost", there is a poster of People  Magazine. On the top of the poster there is a box that says "Matt  Hagan: Man of a Million Faces". Matt Hagan becomes the villian,  Clayface, (appears in Feat of Clay parts 1 and 2) who can change his  physical appearence (as well as create objects such as axes or  hammers from his hands). The People Magazine is dated October 19,  1992 which was the air date of the episode "Perchance to Dream".  Additionally, the shadow of The Grey Ghost is Batmans shadow.