Continuity mistake: When Bova is bringing the baby twins to Django and Marya's house, the arm she is carrying the respective twin in changes depending on the shot. When she is first shown walking towards the house, she is holding Wanda in her left arm and Pietro in her right. When she is walking up the steps to the door, she is carrying Pietro in her left arm and Wanda in her right. When the shot changes after Django opens the door, the twins have switched arms again, and then again when she hands the babies to Django and Marya.
Continuity mistake: When Xavier is surrounded by a group of mutants in his subconscious, if you look at Quicksilver you can see that the colorist made his shirt flesh-colored. You can tell he is supposed to be wearing a shirt because the lightning bolt design is still going across his torso.
Continuity mistake: During the battle at the end, Cyclops uses the crystal statue he brought with him in the fight by throwing it into the air and uses it to refocus his optic blasts on a crowd of attackers. After the battle is over he gives the statue to Dr. Prescott without ever having retrieved it.
00:18:55 - 00:20:20Phaneron
Continuity mistake: When the biker discovers the children hiding in the tree, his motorcycle is parked right next to the tree with the left side of his motorcycle facing the pit. When he gets back on the motorcycle, it is suddenly several feet away from the tree and the front wheel is facing the pit.
Continuity mistake: When Leech is first shown in his sick bed, he is shirtless and under the sheets. When he begins receiving a blood transfusion from Wolverine, he is fully clothed and also wearing a beanie. Given the weak and near-death state he was in, it's extremely unlikely the other Morlocks would bother dressing him.
00:09:20 - 00:14:15Phaneron