[Update: We’ve now learned from trusted sources four more actresses who are testing for the role of Domino in Deadpool 2, in addition to the six we reported previously: Mackenzie Davis (Halt and Catch Fire), Ruby Rose (Orange Is the New Black), Eve Hewson (The Knick), and Kelly Rohrbach (Baywatch). Our original story follows below.]

While the sequel doesn’t yet have a firm release date, development is moving right along on Deadpool 2, and director Tim Miller and the film’s producers are now looking towards casting a key female role. Sources close to the production exclusively tell Collider that testing has begun for the character of Domino, and the actresses under consideration include Lizzy Caplan (Masters of Sex), Mary Elizabeth Winstead (10 Cloverfield Lane), Sienna Miller (American Sniper), Sofia Boutella (Star Trek Beyond), Stephanie Sigman (Spectre), and Sylvia Hoeks (Overspel). There could be other actresses included in the mix, but sources tell us that at least these six performers have tested or are going to test for the role.

Like Deadpool, Domino is a mercenary and a mutant, and her powers include the ability to initiate random telekinetic acts that turn probability in her favor. Additionally, she has a close connection to the mutant Cable, as her comics history found her becoming a partner, confidante, and lover of the mutant and frequent frenemy of Deadpool. It was previously confirmed during the post-credits sequence for Deadpool that Cable will appear in Deadpool 2, so the inclusion of Domino in the sequel as well makes sense.

This shortlist is a mix of established actresses and up-and-comers. Folks like Winstead, Caplan, and Miller have long resumes and at least some experience with action, while Sigman portrayed a Bond girl in Spectre, starred on the FX drama series The Bridge, and stars on the Netflix series Narcos. Netherlands native Hoeks, meanwhile, is poised to make her major American debut in Denis Villeneuve’s sequel Blade Runner 2049.

With word that testing for the role of Domino has begun, we can also safely assume that Miller and Co. have either already found their actor to play Cable, are mulling over a shortlist of actors, or are about to initiate a search.

Deadpool still stands as the biggest surprise of 2016, with the R-rated superhero movie pegged for a solid mid-range box office debut back in February, only to demolish all expectations with a massive $132 million opening weekend. The film went on to gross $782.6 million, and with Miller, screenwriters Rhett Reese and Paul Wernick, and Ryan Reynolds all confirmed to return, fans are certainly hopeful that the sequel will continue the irreverent spirit of the first film.

Filming on Deadpool 2 is aiming to get underway in early 2017, but the lack of an established release date is a good sign—it signals that Miller and Co. are being afforded the time to get the sequel right instead of chasing a date. With the search underway for Domino, however, this thing is certainly getting much closer.