Here is every character who was recast in Fox's The New Mutants.
Even during the original X-Men trilogy directed by Bryan Singer and Brett Ratner, which featured the same actors playing the main X-Men and villains throughout the trio of films, the cracks were evident in of the consistency of casting ancillary characters. Some mutants who were merely background characters in the first X-Men film, like Pyro, Kitty Pryde, and Colossus, took on greater importance in the sequels and were recast with new actors. X-Men Origins: Wolverine then recast the villainous roles of Sabretooth and Col. William Stryker but it also reintroduced a young Cyclops (with a different actor) and Professor X, throwing the timeline into confusion.
Some X-Men: The Last Stand. Lastly, Ryan Reynolds played a bizarre version of Deadpool in X-Men Origins: Wolverine but successfully campaigned to star in a more comic book accurate version of the Merc With a Mouth in two wildly successful Deadpool films.
Professor X
Patrick Stewart played Professor Charles Xavier AKA Professor X in five films: X-Men, X2: X-Men United, X-Men: The Last Stand, X-Men: Days of Future Past, and Logan, as well as cameos in X-Men Origins: Wolverine and in The Wolverine's end-credits scene. Stewart's version of Professor X also has the distinction of dying twice in two different timelines (as well as an unexplained resurrection).
In the revised timeline that began with X-Men: First Class, James McAvoy took over the role of Professor X and he also starred as the mutant psychic in X-Men: Days of Future Past, X-Men: Apocalypse, Dark Phoenix, and he also had a cameo as Xavier in Deadpool 2. Laurence Belcher plays the young Charles Xavier in X-Men: First Class. In addition, Harry Lloyd played a different version of Charles Xavier in FX's Legion, which was set in a completely different timeline from the X-Men films.
Magneto
The role of Erik Lensherr AKA Magneto was originated by Ian McKellan, who would star as the magnetic mutant terrorist in X-Men, X2: X-Men United, X-Men: The Last Stand, and X-Men: Days of Future Past. McKellan's Magneto also has a cameo in The Wolverine's end-credits scene. Brett Morris plays the young Erik in X-Men's flashback scenes at Auschwitz.
Michael Fassbender was cast as Magneto in the revised timeline and he played Lensherr in X-Men: First Class, X-Men: Days of Future Past, X-Men: Apocalypse, and Dark Phoenix. In addition, Bill Millner plays the young Erik in First Class' flashback scenes at Auschwitz.
Mystique
Raven Darkholme AKA Mystique was radically reimagined from the Marvel Comics and Rebecca Romjin portrayed the stealthy blue shapeshifter in X-Men, X2: X-Men United, X-Men: The Last Stand, and she also briefly cameos in X-Men: First Class.
Jennifer Lawerence took over the role for X-Men: First Class, X-Men: Days of Future Past, X-Men: Apocalypse, and Dark Phoenix, while Lawrence's version of Mystique was reconceived to become one of the most pivotally important mutants in the revised X-Men timeline. Morgan Lily also played the young Raven in X-Men: First Class.
Cyclops
Three different actors have played three different versions of Scott Summers AKA Cyclops in the X-Men movies. James Marsden played the role of the X-Men's ocular field commander in X-Men, X2: X-Men United, and X-Men: The Last Stand. Tim Pocock played the young Scott Summers in X-Men Origins: Wolverine. Finally, Tye Sheridan played Cyclops in X-Men: Apocalypse and Dark Phoenix, and he also had a cameo in Deadpool 2.
Jean Grey
The pivotal role of Jean Grey, who transformed into Dark Phoenix in both X-Men timelines, was originated by Famke Janssen, who played the mutant psychic in X-Men, X2: X-Men United, X-Men: The Last Stand, and The Wolverine. The young Jean was played by Haley Ramm in X-Men: The Last Stand.
Sophie Turner took over the role of Jean Grey in X-Men: Apocalypse and Dark Phoenix, while the younger version of this Jean Grey was played by Summer Fontana in Dark Phoenix.
Storm
Halle Berry originated the role of Ororo Munroe AKA Storm in X-Men, X2: X-Men United, X-Men: The Last Stand, and X-Men: Days of Future Past. The role was then recast with Alexandra Shipp, who played the mutant mistress of weather in X-Men: Apocalypse, Dark Phoenix, and she also had a cameo in Deadpool 2.
Henry "Hank" McCoy made his first appearance in X-Men: The Last Stand where he was played by Kelsey Grammer, who also reprised the role at the end of X-Men: Days of Future Past. In the revised X-Men timeline, the furry blue mutant genius was played by Nicholas Hoult, who starred as Beast in X-Men: First Class, X-Men: Days of Future Past, X-Men: Apocalypse, Dark Phoenix, and he also cameoed in Deadpool 2.
Nightcrawler
Kurt Wagner AKA Nightcrawler made a memorable debut in X2: X-Men United, where he was played by Alan Cumming. Nightcrawler made his return in the revised X-Men timeline where he was played as a teenager by Kodi Smit-Mhee in X-Men: Apocalypse. Smit-Mhee returned as Nightcrawler in Dark Phoenix and he had a cameo in Deadpool 2.
Sabretooth
Tyler Mane played Victor Creed AKA Sabretooth in X-Men, where he was a henchman of Magneto and a member of the Brotherhood of Mutants. The role was recast with Liev Schreiber in X-Men: Origins Wolverine, and this version of Sabretooth was retconned to be the half-brother, oldest friend, and arch-enemy of Wolverine.
Kitty Pryde
Three different actors have played Kitty Pryde, who has the mutant power of phasing (i.e. walking through walls). Sumela Kay played Kitty in X-Men and Katie Stuart took over the role in X2: X-Men United. But these were mere cameos and when Kitty was promoted to become a principal character, Ellen Page was cast as the phasing mutant. Page played Kitty in X-Men: The Last Stand and she reprised the role in X-Men: Days of Future Past, where Kitty also got the new mutant ability to send Wolverine's mind back through time.
