Random Trivia For This Title:
- [?] Wil Traval and [?] Paul Mescal were rumored for roles.
- [?] Rarmian Newtown was rumored for either Mimic or Shane and Toby Huss for the role as the Shi'ar character, Mentor.
- In the reshoot, director Simon Kinberg changed the original movie villains' alien race from the Skrulls to the D'Baris. The character played by Jessica Chastain became Vuk, a member of the D'Bari.
- This is the fourth movie that James McAvoy had to shave his head for, the first three being X-Men: Apocalypse (2016), Split (2016), and Glass (2019).
- Olivia 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 Turner studied mental illnesses in preparation for playing the Dark Phoenix.
- Tye Sheridan admitted shortly before the film's release that he wore a "muscle suit" throughout production instead of working out.
- 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)).
- The role of Vuk was first offered to Angelina Jolie who passed on it before Jessica Chastain accepted it. Jolie passed on the role because she was more interested in playing the titular character in Bill 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 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 Muschietti, for the lead role of the Losers' Club Bill Denbrough.
- This is Jessica 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 Lawrence is now actually older than Rebecca Romijn was when she originated the role in X-Men (2000).
- 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 the first X-Men film to not feature or reference either Logan/Wolverine or the actor who portrays him, Hugh 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).
- Hans Zimmer decided to retire from composing superhero movies after having worked on scores for Batman, Superman, Wonder Woman, and Spider-Man, but Simon Kinberg convinced him to work on this film.
- 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.