Revealing mistake: In the scene where Storm and Nightcrawler rush to rescue the children from the holding cell, you see a shot of the cell where the children stand up and say "Listen..." before Nightcrawler teleports inside. If you look carefully, you will see Nightcrawler's silhouette in the shadow against the wall. (01:27:50)
Revealing mistake: After Toad spits his slime at Jean Grey he falls to the floor. You can see the tether that was holding him in mid air. (01:13:55)
Revealing mistake: In the scene in the laboratory under the mansion, when Wolverine confronts Jean about Cyclops, there is a close up shot of Wolverine's hand holding Cyclops' glasses. In this shot there is a small cut visible on Wolverine's hand - his healing power should not allow this.
Revealing mistake: When the old couple who give Wolverine clothes are first driving towards their house, there is an aerial shot of them driving over a bridge. This is supposed to be set in Canada (drive on the right) but it was filmed in New Zealand (drive on the left). They are driving on the right but the arrow on the road is on the left side.
Revealing mistake: In the funeral scene where Dr. Viper Lady is videoing Logan fighting, she starts lowering the smartphone, but the "faked" image on the screen doesn't change to match her arm dropping down.
Revealing mistake: In the submarine, when Emma goes to get ice for Shaw, Azazel's tail is missing when he helps pull the submarine's ladder down.
Revealing mistake: When Apocalypse first introduces himself to Magneto in the factory and tries to persuade him to join his side, a seam in Apocalypse's facial prosthetics next to his mouth is starting to come apart during a close-up shot.
Revealing mistake: Near the end when the orphans are exiting the building in the bus, you can tell they practised the sliding part. There are marks in the roof of the bus from previous takes.