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 the three horsemen are climbing onto their mechanical horses, Famine's horse is in the middle, and Pestilence's horse is on the right. Once all three have all been individually shown to be mounting their horses, Famine and Pestilence have swapped places. (00:06:08)
Continuity mistake: When Archangel is lamenting his actions, the communicator devices from Storm's uniform are missing. (00:20:15)
Continuity mistake: When Storm is first watching the World Peace Conference on TV, she is sitting on a couch in a rec room. Moments later, she is watching in a hallway while standing. (00:07:45 - 00:09:00)
Continuity mistake: When Storm is watching TV with her arms folded, her left hand shows her index and middle fingers touching. When the shot changes, it is her middle and ring fingers that are touching. (00:08:40)
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 Apocalypse is ordering War and Archangel to attack the tanks, Archangel's decollete is the same light blue color as his skin, when it should be the darker shade of blue that his outfit his, since his outfit leaves his face and hands exposed. The photograph Xavier shows Rogue of Archangel later in the episode also depicts the same error. (00:09:30 - 00:11:12)
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 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 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 the cameraman drops his camera, it lands on the ground and rests on a rock so that the lens is at a slanted angle. When the shot changes to the camera's point of view, it shows Apocalypse right side up, when he should be slanted to correspond with the camera. (00:10:14)
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 Storm turns on the TV, the news reporter's microphone has a yellow 7 on a black circle. A couple of shots later, the black circle is now also yellow. (00:07:49)
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 Storm turns on the TV, much of the Eiffel Tower is in the background. A couple of shots later, the reporter is standing in front of a building that would obscure much of the Eiffel Tower, and is also suddenly standing next to a news van. (00:07:47)
Continuity mistake: When Mystique, disguised as Warren Worthington, first walks into the bar, the walls are purple. When she is saying "You don't have to be mutants," the walls are now red. When the shot changes, they are back to being purple, and a framed picture has appeared over her left shoulder. (00:04:18)
Continuity mistake: When Rogue, Cyclops, Jean Grey and Xavier are first shown in the bar, the glasses in front of Rogue and Cyclops contain green liquid. When Cyclops is consoling Rogue, the liquid is now blue. When the shot changes, the liquid in the glass in front of Rogue is now green again. (00:03:49 - 00:04:18)
Continuity mistake: When the Lady Gardener kills the rose, it droops down almost to the surface of the table. When the shot changes, it is now only drooping about midway down its vase. (00:03:56)
Continuity mistake: When Warren Worthington is strapped to the table, the arm and leg restraints are gold. After the table has been lowered, the restraints are now silver. (00:02:29 - 00:02:56)
Continuity mistake: When the conference chairman is first shown at the podium, there are five microphones attached to it. A few shots later, there are only four. (00:07:55)
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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