|Although this article is based on canonical information, the actual name of this subject is conjectural.|
Shadow Casters were images similar to shadow puppets, and meant to be used for a shadow play.
The Slayer, Nikki Wood, owned a mystical set of shadow casters that told the origin story of the very first Vampire Slayer, Sineya. Following Nikki's death, the shadow casters were left to her son, Robin.
During the battle against the First Evil, Robin passed the shadow casters to Buffy Summers. The casters were set in motion by Xander, with the help of Dawn, who read the instructions through a tome that came with the set. Once set, the shadow casters moved on their own accord and were able to create a portal through time and space, sending Buffy to the era of the Shadow Men, and leaving a demon in exchange.