Random Trivia For This Title:
- The third act was originally going to take place in space. After re-shoots were completed, it was changed to a sequence where the X-Men are kidnapped and taken aboard a military train.
- Hans ZimmerHans Zimmer decided to retire from composing superhero movies after having worked on scores for Batman, Superman, Wonder Woman, and Spider-Man, but Simon KinbergSimon Kinberg convinced him to work on this film.
- This is the first X-Men film to not feature or reference either Logan/Wolverine or the actor who portrays him, Hugh JackmanHugh Jackman. This is because Jackman retired from the role, which he portrayed since X-Men (2000). He was briefly featured in Deadpool 2 (2018) through reused and stock footage from X-Men Origins: Wolverine (2009).
- The mutant singing during the mutant school party is Alison Blaire a.k.a. Dazzler, a mutant from the comics who can change sound into light, a talent she used to further her pop-singer career.
- This is Jessica ChastainJessica Chastain's first Marvel film. She previously turned down the roles of Maya Hansen in Iron Man 3 (2013) and Hope Van Dyne in Ant-Man (2015).
- In her role as Mystique, Jennifer LawrenceJennifer Lawrence is now actually older than Rebecca RomijnRebecca Romijn was when she originated the role in X-Men (2000).
- The role of Vuk was first offered to Angelina JolieAngelina Jolie who passed on it before Jessica ChastainJessica Chastain accepted it. Jolie passed on the role because she was more interested in playing the titular character in Bill CondonBill Condon's Bride of Frankenstein project before Universal decided to put it on hold. Interestingly, they were the only names considered by the studio, and both were suggested by James McAvoyJames McAvoy due to his working relationship with them. To return the favor, Chastain recommended McAvoy to her friend, producer [?] Barbara Muschietti, and her brother, It: Chapter Two (2019) director Andy MuschiettiAndy Muschietti, for the lead role of the Losers' Club Bill Denbrough.
- Charles Xavier is the only character that appears in all [X-Men movies] (considering the post credit scene in The Wolverine (2013) and cameo appearance in X-Men Origins: Wolverine (2009)).
- Olivia MunnOlivia Munn was set to return as Psylocke, but ultimately was unable to reprise her role due to scheduling conflicts with filming The Predator (2018).
- Sophie TurnerSophie Turner studied mental illnesses in preparation for playing the Dark Phoenix.
- Tye SheridanTye Sheridan admitted shortly before the film's release that he wore a "muscle suit" throughout production instead of working out.
- In the reshoot, director Simon KinbergSimon Kinberg changed the original movie villains' alien race from the Skrulls to the D'Baris. The character played by Jessica ChastainJessica Chastain became Vuk, a member of the D'Bari.
- This is the fourth movie that James McAvoyJames McAvoy had to shave his head for, the first three being X-Men: Apocalypse (2016), Split (2016), and Glass (2019).
- [?] Wil Traval and [?] Paul Mescal were rumored for roles.
- [?] Rarmian Newtown was rumored for either Mimic or Shane and Toby HussToby Huss for the role as the Shi'ar character, Mentor.