From Variety on the new villain and heroes:
If the new spinoff is picked up to series at the CW — which seems like a safe bet, given the success of its predecessors — it will feature previously established heroes and villains from “Arrow” and “Flash,” including “Arrow’s” Brandon Routh, as Ray Palmer/the Atom; Caity Lotz, who portrayed the (seemingly dead) Sara Lance/Black Canary; “The Flash’s” Victor Garber as Dr. Martin Stein/one half of Firestorm (Ronnie Raymond, the other half of Firestorm played by Robbie Amell, was not announced as part of the spinoff’s lineup), Wentworth Miller as villain Leonard Snart/Captain Cold, and Dominic Purcell as his partner in crime, Mick Rory/Heat Wave. The show will also introduce at least three major DC Comics characters who have never been in a television series before.Deadline broke the news that Dominic Purcell ("Heat Wave" on THE FLASH) has joined the spinoff cast:
Both “Arrow” and “Flash” have already featured some of DC’s most iconic villains, including Ra’s al Ghul, Deathstroke and Reverse Flash, and it was important for Berlanti to find someone equally worthy for the new spinoff, which means he’s focusing on “making sure that the villain that we have on that show is distinct too… another big character who hasn’t been used yet.”
EXCLUSIVE: Another popular recurring DC character from the Arrow-Flash universe is boarding the CW’s proposed spinoff from the two superhero dramas. The new Flash villainous duo of Captain Cold/Heat Wave will be staying intact as Dominic Purcell has joined Brandon Routh, Wentworth Miller, Victor Garber and Caity Lotz in the superhero team-up show from Arrow creators Greg Berlanti, Andrew Kreisberg and Marc Guggenheim.The untitled spinoff is set for a midseason 2016 launch - are you ready?
Purcell will reprise his role as Mick Rory, a pyromaniac who finds an outlet for his obsession with fire when he teams up with Leonard Snart/Captain Cold (Wentworth Miller) and becomes the villain known as Heat Wave. The new project, eyed for a midseason launch next season, extends the Flash reunion of Prison Break stars Miller and Purcell and would mark the first series regular gigs for both actors since the cult Fox drama.