Although not in the movie, Sir Patrick Stewart jokingly informed Bryan Singer that he would be willing to play Mystique, should Jennifer Lawrence "start playing up." He said: "I am so ready to be naked, painted blue, and the world is ready for it too."
In the comics, Mystique is the mother of Nightcrawler, and was forced to abandon him, though this is never acknowledged or hinted at in either this film or X2: X-Men United (2003). However, in an outtake, Jennifer Lawrence ad-libbed a line acknowledging Nightcrawler as her son by Azazel; this take is shown in the gag reel.
Particularly with Psylocke, Nightcrawler, and Cyclops, the outfits and characters' looks were designed to pay homage to their comic book counterparts, differently from past films when the X-Men used standard black leather uniforms. Cyclops' costume is taken from Jim Lee's blue and yellow design in the 90s.
This is the first time that the Summers brothers, Scott Summers (Cyclops) and Alex Summers (Havoc), appear together in a live-action movie. In the comics, there was another brother, Gabriel Summers (Vulcan), but he has not appeared in any shows or movies, and the filmmakers decided two brothers in a film was enough.