Since before Season 2 of the CW hit The Flash there have been rumors of Mirror Master appearing in the series. Mirror Master is of course one of the Flash’s greatest foes, being able to travel into any reflective surface to a place called the Mirror World. The Mirror World allows him to travel to parallel universes, very similar to Earth-2. With Earth-2 being introduced in Season 2, the creators must have wanted to wait on Mirror Master.
Grey Damon has been cast as Sam Scudder. Damon has appeared in several TV series on multiple networks. This is the official announcement from WBTV.
“One of the Flash’s most infamous Rogues, Sam Scudder — aka Mirror Master — is a smooth criminal with a huge ego. Upon discovering he now has the power to travel through any reflective surface, Scudder embarks on a massive crime spree to prove himself the greatest thief that Central City has ever seen.”
Scudder will first appear in the fourth episode of Season 3, which will focus heavily around the Flashpoint storyline. It is still unknown if he will become one of the Rogues with Captain Cold, Heatwave, and Weather Wizard like in the comic books or if he will appear in more than one episode.
The Flash Season 3 premieres October 4th, 2016 on the CW.
Source: Comic Book Resources