Random Trivia For This Title:
- The lapel pin that Dr Reyes wears on her lab jacket has the same red diamond that X-Men villain Mr. Sinister has on his forehead. Mr. Sinister's real name is Nathaniel Essex, and it is revealed, later in the movie, that the facility is run by the Essex Corporation.
- Jon HammJon Hamm was cast to portray Nathaniel Essex / Mister Sinister, with filming for the role completed, though his role was cut from the film as a result of an extensive reshoot process that changed elements of the film.
- Nat WolffNat Wolff was considered for the role of Cannonball.
- Rosario DawsonRosario Dawson was originally offered to played Cecilia Reyes but dropped out for unknown reasons.
- The filmmakers cite the films One Flew Over the Cuckoo's Nest (1975), The Shining (1980) The Breakfast Club (1985) and A Nightmare on Elm Street 3: Dream Warriors (1987) as an influence on the film's production design, due to the closed-in settings each film used for dramatic purposes.
- The alien mutant Warlock was planned to appear in the film, with Sacha Baron CohenSacha Baron Cohen in talks for the role, but his powers would have been too expensive for the film's budget, so he was removed with the intent to appear in a sequel.
- The filmmakers described the film as "a haunted-house movie with a bunch of hormonal teenagers," and cite the works of horror storyteller Stephen KingStephen King and teen drama filmmaker John HughesJohn Hughes as an influence.
- According to Josh BooneJosh Boone, the film was originally to be set during the events of X-Men: Apocalypse (2016), and would feature a cameo by Professor X (James McAvoyJames McAvoy) and Storm (Alexandra ShippAlexandra Shipp). The script was rewritten to remove these elements, but Boone felt the film was not largely affected by this change: "it might as well be the '80s in terms of the setting."
- The majority of the film was shot on location at Medfield State Hospital, in Massachusetts. This hospital was the state's first mental asylum, and most of the cast and crew were unsettled by the location.
- This film features four members of the original New Mutants group (Cannonball, Mirage, Sunspot, Wolfsbane), with Magik being a member from the second roster.
- Josh BooneJosh Boone admitted that he found shooting to be stressful, as he felt "a bit neutered" because he had to tone down the film from his original "full horror" ideas.
- Josh BooneJosh Boone intended this film to be the first in a trilogy, with the second film to be an alien invasion movie featuring the alien mutant Warlock, and then the third and final installment to be a supernatural, apocalyptic horror movie based on the X-Men comic event "Inferno" (demons invade the Earth and Magik plays a major role).
- The scenes from [Buffy the Vampire Slayer] foreshadow events in the movie: Willow and Tara kissing prior to Dani and Rayne doing the same, and Buffy fighting the grinning Gentlemen before the mutants face the Smiling Men.