Rebecca Romijn is making a comeback as Mystique in the upcoming Marvel Cinematic Universe film, Avengers: Doomsday, slated for release on December 18, 2026. The actress, who originated the role in the X-Men trilogy in the 2000s, has expressed her surprise and excitement about reprising the fan-favorite mutant.

Romijn described receiving the call to be part of Avengers: Doomsday as "very surreal" and "unexpected". She is currently in the midst of filming for the highly anticipated project and said the whole experience has been "wonderful" so far. She first played Mystique in the 2000 film, X-Men. Romijn returned to play the character in 2003, and her final presence as Mystique onscreen was in 2006, for the film X-Men: First Class.

Speaking at San Diego Comic-Con, Romijn revealed that the script for Avengers: Doomsday is still being written even as filming is underway. "The script hasn't — they haven't finished writing it," she said. "It's been very, very fun, and we don't know yet. They keep everything very close to the vest themselves in an effort to keep everything under wraps". She did not confirm or deny if she had read the entire script and would not reveal which actors she filmed scenes with.

Marvel Studios President Kevin Feige has addressed the studio's approach to script development, emphasizing their culture of constant evolution, which he refers to as "plus-ing". He stated that while Marvel never starts filming without a script, they are always open to new ideas and adjustments during production. According to Feige, "There's 'plus-ing' occurring on the set of Avengers: Doomsday as we speak… because what those filmmakers, those actors, both the ones that are playing these characters for the first or second time and the one playing them for the 10th or 12th time, are the best in the world at it, and know these characters so well".

Romijn also reflected on the "surreal" experience of stepping back into the blue body paint nearly two decades after X-Men: The Last Stand. "It was very surreal to be with my old cast as well as a new cast," she said. "I had crazy dreams while I was there for a large chunk of shooting. Like, really kind of regressive dreams… It was very strange, my brain was really trying to organize. Like, wow, this is a character I played 25 years ago, 20 years ago".

Avengers: Doomsday will see the return of other original X-Men stars, including Patrick Stewart as Professor X, Ian McKellen as Magneto, James Marsden as Cyclops, and Alan Cumming as Nightcrawler. Robert Downey Jr. will also be returning to the MCU but in the avatar of supervillain Victor Von Doom aka Doctor Doom. The film is expected to bring together characters from various films, including The Fantastic Four: First Steps, Thunderbolts, and Black Panther.

Romijn also stars in the third season of Star Trek: Strange New Worlds as Commander Una Chin-Riley. As a mother, Romijn consciously chooses roles that serve as positive role models for her daughters and young girls watching globally.