Goofs

• Miscellaneous: In the closing credits, the credit for Paint Foreman is misspelled as Paint Forman.
• Revealing mistakes: When Beast meets Leech, a close-up of Beast's face as he remarks on Leech's power reveals the net-like tape used to attach the blue fur to his face.
• Revealing mistakes: When Wolverine shows Jean Scott's glasses when he is trying to control her, a close-up of his hand reveals a small cut on one of his fingers. In the X-Men universe, Wolverine has healing powers that prevent him from having any cuts on his body for any significant length of time.
• Miscellaneous: While Jean Grey was tearing off Wolverine's skin, in the last and the biggest tear off, despite Wolverine has restored completely, when Jean Grey starts to tear off, the wounds previously occurred have healed in one frame, less than a millisecond.
• Continuity: Time of day during the final battle sequence. The first pan over the bridge from southeast looking north, is clearly midday as the shadow of the bridge is almost directly underneath it. When Magneto first walks onto the Golden Gate bridge it is close to sunset, and the shadowing is very inconsistent, sometimes sharp from direct sunlight, sometimes not. By the time they move the bridge and drops it onto the island, and lowers himself to the bridge, and all the mutants move forward, it is suddenly dark. In the DVD commentary, everyone acknowledges it, but says "Hopefully you're into the movie enough . . ." The whole battle is then shown as taking place in the dark.
• Revealing mistakes: When Wolverine leaves on the motorcycle from the school and goes to the woods looking for Jean, to Magneto's hide-out, he is wearing a brown leather jacket. But, once in the woods, he senses something, the camera pans down as he extends his claws. Although the DVD Commentary from the Writers & Director mention it and jokingly say "He has a mutant power here, the ability to lose his jacket. He has a jacket here, if you look at his sleeve . . . and now, no jacket." This is because right after that he is shown in nothing but the white wife-beater style t-shirt. But if you look at it in slow-motion, and see in subsequent shots, it is actually his watch. In some shots, his jacket hangs as low or lower than the sleeve and if he was wearing it, we would most likely have seen the front part of the jacket against his jeans in that shot.
• Continuity: In the woods at Magneto's hide-out, Wolverine is attacked by the mutant Spike. When he kills Spike, he has two spikes in his stomach on either side of his belly button. The wounds heal, and you see the holes in the wife-beater style t-shirt he is wearing, but in the rest of these scenes, the holes are gone.
• Continuity: When Dr. Kavita Rao prepares The Cure injection for Angel, at first, the needle clearly doesn't have the plastic protective cap on, then she takes it off in the next shot.
• Revealing mistakes: In the scenes of traffic on the Golden Gate Bridge, there are no yellow lane markers separating the northbound and southbound lanes. They are used to adjust the number of lanes in each direction, and they're always present on the bridge.
• Revealing mistakes: On several occasions, the line where Mystique's blue makeup ends around her mouth is easily visible.

Taglines

• Take a Stand
• Po Czyjej Stronie Bedziesz? (Whose Side Will You Stand On?) [Poland]
• Whose Side Will You Be On?
• L'Ultime chapitre de la trilogie (The final chapter of the trilogy) [France]

Trivias

• Philippe Rousselot was hired as cinematographer by Matthew Vaughn, and initially stayed on when Brett Ratner took over as director. Not long into shooting, however, Rousselot quit the project (later saying that signing on to shoot the film was the biggest blunder he'd ever made). Dante Spinotti, the cinematographer on Ratner's previous two films, was available, and he took over for most of the remaining filming. He had to leave about a week before the end of shooting as he was committed to working on The Contract (2006/I), and so J. Michael Muro was hired for the remainder of shooting.
• The "Tracking Mutations" issue of Scientific American that Hank McCoy/Beast is reading in his office while hanging from the ceiling was not a fake prop; the magazine actually had that cover story in October of 2005.
• Angel's wings were initially too heavy for Ben Foster, and were remade from foam.
• Patrick Stewart's "de-aged" effect in the opening scene was based on publicity photos from the first season of "Star Trek: The Next Generation" (1987).
• Halle Berry had initially decided not to reprise her role as Storm for this film, citing lack of character development in the previous two installments and a tense relationship with director Bryan Singer. However, after Singer's departure and suffering a major box-office flop with Catwoman (2004), Berry agreed to return on the condition that her role be expanded. Consequently, in this film Storm serves as leader of the X-Men, which is keeping with the comics since she served as team leader for a time in Xavier's absence.
• When Bryan Singer was still set to direct, he intended the Dark Phoenix storyline as the sole focus of the film. He also intended to feature the villain Emma Frost/White Queen as a major character, with the role intended for Sigourney Weaver. With Singer's departure, the character of Emma Frost was dropped, and the Dark Phoenix story was relegated to a subplot in favor of the "cure" storyline. He also planned on introducing long time fan favorite Gambit into the film, to serve as both the new recruit as well as a romantic rival of Iceman's for Rogue's affection. For the part, Singer had planned on casting Channing Tatum. However, once he left, the script was changed, and Gambit was reduced to a minor cameo, then ultimately dropped from the script.
• The characters Phat and Spike (both from the X-Statix comic book) make cameo appearances.
• Cain Marko's line "Don't you know who I am? I'm the Juggernaut, bitch" was inspired by a popular web parody film that made use of scenes from "X-Men The Animated Series." Throughout the parody , the Juggernaut character repeatedly says, "I'm the Juggernaut, bitch." According to the Wikipedia, Brett Ratner even has a link to this parody on his own website. (Whether or not the parody itself was inspired by a mis-heard line from an old X-Men video game is irrelevant to film's usage of this line, since it's clearly an homage to the web parody)
• Summer Glau auditioned for the role of Kitty Pryde. She looked to Joss Whedon, who gave her a part in "Firefly" (2002) and Serenity (2005), for advice because she knew he was a big X-Men fan, unaware that he had written the "Astonishing X-Men" comic book for Marvel, featuring the storyline about the mutant cure. Her audition script turned out to be pages from issue 5 of Joss Whedon's Astonishing X-Men book.
• Ian McKellen (Eric Lensherr/Magneto) and Patrick Stewart (Professor Charles Xavier) had 20 years shaved off their features for the opening sequence. The filmmakers used digital technology to match current features to those in old photos.