Continuity mistake: When Xavier is briefing the X-Men about Apocalypse, Storm is on Xavier's left, and as the camera pans up and to the left, you can see no-one is around her. When the shot changes, Cyclops and Rogue are suddenly next to Storm. (00:10:21)
Continuity mistake: When Xavier is saying "They can be appealed to, reasoned with," Jean Grey's back is entirely peach-colored, when there should be a blue stripe going down the middle of it. (00:10:36)
Continuity mistake: When Xavier, Jubilee, and Rogue are walking towards the end of the Blackbird's runway, their shadows on the wall show Rogue in front of Jubilee, but Jubilee is actually in front of Rogue. (00:10:51)
Continuity mistake: When Rogue is flying toward Adler's lab, you can see the building is several stories off the ground. When she flies in through the hole in the roof, the interior of the lab is on the top-level, whereas the previous episode showed that the lab was on the ground level. (00:12:55)
Continuity mistake: When Rogue is shackling Dr. Adler to the platform, she only applies the restraints to his arms and left foot, leaving the right foot unshackled. Moments after Adler reveals himself to Rogue to being Mystique, the right foot is now shackled as well. (00:13:31 - 00:14:08)
Continuity mistake: When Rogue is interrogating Mystique, she is standing in various places next to the platform depending on the shot. (00:13:45 - 00:14:08)
Continuity mistake: When Rogue positions the platform that Mystique is shackled to upright, Mystique's feet are close to touching the floor. A couple of shots later, her feet are suddenly several inches higher. (00:14:08)
Continuity mistake: When the statue is about to fall on Wolverine, his arms are colored yellow. (00:16:25)
Continuity mistake: The trap door that Apocalypse uses to escape suddenly disappears once Wolverine tries to claw his way through it. (00:19:35)
Continuity mistake: When Archangel is lamenting his actions, the communicator devices from Storm's uniform are missing. (00:20:15)
Answer: Chris Potter, the original Gambit voice actor, did indeed quit the role in the 4th season. His last episode was The Phalanx Covenant Part 1 so it seems reasonable that Fox would limit the use of the character even though it was recast. It doesn't appear that Potter left the role due to animosity, he stated in an interview that he wished to play Gambit in the first live action X-Men film.
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