While The CW's Arrow/Flash Spinoff may not have a title quite yet, the cast keeps growing by the day, with Dominic Purcell signing on to play his Flash villain Heat Wave in the series, which is being targeted for a midseason debut. Dominic Purcell joins a cast that includes Heat Wave's villainous partner Captain Cold (Wentworth Miller) and Firestorm (Victor Garber) from The Flash, along with Arrow's Atom (Brandon Routh) and Caity Lotz in an unspecified role. The show will also mark the first series regular gigs for Dominic Purcell and Wentworth Miller since they both starred together on the Fox drama series Prison Break, which ran for four seasons between 2005 and 2009.

Leonard Snart, a.k.a. Captain Cold, first appeared in the show's fourth episode "Going Rogue" by himself, but he returned in January's "Revenge of the Rogues" with his new partner Mick Rory, a.k.a. Heat Wave. Mick is a pyromaniac who is obsessed with fire and brandishes a special heat gun developed by S.T.A.R. Labs' Cisco Ramon (Carlos Valdes) that was eventually stolen and given to Mick by his friend Leonard Snart. Both Wentworth Miller's Captain Cold and Dominic Purcell return to The Flash in tonight's episode, "Out of Time".

The initial announcement of this untitled series last month also mentioned the spinoff will feature three major DC Comics characters who haven't been featured in a TV series before, but we still have no word on these characters' identities. It's also unclear whether or not Caity Lotz will return as Black Canary, since she was killed off in the Arrow Season 3 premiere, of if she is playing another character entirely. Deadline also reports that Victor Garber, who plays Dr. Martin Stein, one half of Firestorm, will not be joined by the other half, Ronnie Raymond, since Robbie Amell did not sign on for the project.

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Arrow and The Flash executive producers Greg Berlanti, Andrew Kreisberg and Marc Guggenheim created the untitled spinoff series, although it isn't known when production may get under way. The writers will executive produce with Sarah Schechter. Are you glad that both Heat Wave and Captain Cold will be pairing up again for this Arrow and The Flash spinoff? Let us know what you think below.