- Taylor Schilling, Crystal Reed, Rebecca Rittenhouse, Jessica De Gouw, and Sarah Greene screen-tested for the role of Vanessa Carlysle before Morena Baccarin was cast.
- Daniel Cudmore was offered to reprise his role as Colossus from X2: X-Men United, X-Men: The Last Stand, and X-Men: Days of Future Past for the film. However, Cudmore declined the offer, as he was unhappy with the idea of only doing motion capture work while another actor dubbed over his lines.
- Robert Rodriguez was originally approached to direct the movie before Tim Miller was hired, but turned it down in order to helm Spy Kids: All the Time in the World.
- There were plans for cameos from various other X-Men, including Hugh Jackman as Wolverine, but the studio denied all of them for being too expensive.
- An earlier draft of the film surfaced online, and while similar to the finished film, did not feature Angel Dust or Negasonic Teenage Warhead. Additionally, Garrison Kane, Wyre, and Sluggo were all supposed to appear as Ajax's enforcers. Due to budgetary issues (with the CGI required for Kane's cybernetic arms proving especially expensive), the three villains were combined into Angel Dust, who takes Sluggo's place as the one who fights Colossus during the final battle.
- Miller and the writers considered having Cannonball as the teenage X-Men member partnered with Colossus, with Miller saying he would have been written as a "stupid hick" character. They decided to use Negasonic Teenage Warhead instead, as they felt Cannonball was too silly to work as a Straight Man to Colossus and Deadpool.
- Related to this, the writers would have originally had to have Negasonic Teenage Warhead's power set be more similar to the comics, as they did not have the rights to change it at first. What did they do? They went to Marvel Studios to ask permission for this to happen. By sheer coincidence, Marvel themselves had wanted to use certain charactersnote that 20th Century Fox had the rights to. It worked out well in the end: Marvel got the rights to Ego, while Fox could change NTW's power set.
- Director Tim Miller has said the tone shifted several times in development, with the studio looking for a PG rating at one point.
- Early drafts of the script featured a joke where it would have been revealed that Deadpool's mask was actually a store-bought Spider-Man mask that had been turned inside out. This was presumably cut due to potential legal issues (as Spider-Man's film rights are owned by Sony).
- There was going to be a Running Gag involving Wade and the other bar patrons betting money on how Amy Winehouse would die. This was cut because Winehouse actually did die sometime after the script was written, making the joke both irrelevant and possibly insensitive.
- Patch originally appeared in the script as a bartender, and would have been strangled to death by Wyre when Ajax and his men stormed the bar. His role was ultimately given to Weasel.
- There was going to be a Sequel Hook revealing that Ajax was actually just a puppet working for Doctor Killebrew, the real mastermind behind the experiments that mutated Wade.
- Cable almost made it into the movie, but it was decided that his introduction would work better in a sequel.
- The gag involving the Deadpool action figure from X-Men Origins: Wolverine and the WHAM! album was originally slightly different, and was more of a Take That!.
- The original plan for the stinger was yet another Call-Back with Deadpool finding Beast shitting on his lawn and chasing him off. They even went so far as to approach Nicholas Hoult, who absolutely loved the idea, but again it proved too expensive.
- Taskmaster was in the script at one point, but like the above instances, was cut for being too expensive, especially since Marvel still owns the rights for him.
- Bob was originally meant to be the actual Bob from HYDRA, but a combination of the film's limited budget and possible legal action from Marvel forced the writers to take out any explicit references to HYDRA.
- The writers and director had to figure out how to trim $7 million out of the film's budget in 48 hours, or else production couldn't begin. While in most instances this is a sign of a Troubled Production (especially given the production troubles of Fantastic Four (2015), filmed around the same time), everyone thought the changes made the movie much tighter. The deletions they made included:
- The condensing of Wyre, Garrison Kane, and Sluggo down into Angel Dust.
- A motorcycle chase between Ajax and Deadpool.
- A pitched gun battle at the scrapyard, which was solved by introducing the Running Gag of Deadpool forgetting his ammo bag in the taxi.
- Other pitches for the end credits included a 1980s Knight Rider style version, and an Honest Trailers version done by the actual crew of the web series.
- Ajax was supposed to be scarred by Wade, who puts "Hi, my name is Francis" on his forehead and get arrested after the fight with Wade.
- Wade was orginally supposed to Mercy Kill Worm.
What Could Have Been / Deadpool (2016)