Continuity mistake: When Gambit is avoiding the electrified coils in the Danger Room, his normally black and red eyes are colored like a normal person and his gloves are entirely fingerless whereas they are usually only fingerless for the thumb, index and pinkie fingers. (00:02:15)
Character mistake: When Rogue asks Storm what her plan is for dealing with the closing walls, Storm says "You three stop the walls, I shall slow the ceiling." Besides Storm and Rogue, Jubilee, Jean Grey, and Gambit are also there, so Storm should have said "You four stop the walls." (00:03:12)
Continuity mistake: When the walls begin closing in on the X-Men in the Danger Room, the blue center of Jean Grey's outfit is incorrectly colored the same light-orange color as most of her outfit. (00:03:12)
Continuity mistake: When Storm is having a flashback to her childhood in a fit of claustrophobia, she is depicted as a Caucasian girl with red hair. (00:03:35)
Continuity mistake: When Rogue is thrown into the wall by Storm's wind, the green side of her uniform is incorrectly colored yellow. (00:03:52)
Continuity mistake: When Jean is first shown in her dress, it is a solid pink color. When she is walking down the sidewalk on her date with Cyclops, the midsection of her dress is now a lighter shade of pink than the rest. (00:04:34 - 00:05:18)
Continuity mistake: When Jean Grey is first shown standing in Wolverine's doorway, her arm is resting on the door with her elbow level with her shoulder. When the shot changes, her elbow is now level with her breasts. (00:04:34)
Continuity mistake: When Jean is walking out of Wolverine's room, part of her dress around her abdomen briefly changes to a lighter shade of pink. (00:04:57)
Continuity mistake: When Jean and Cyclops are kissing after he tells her his mind is on nothing but her, he is wearing a gray suit jacket, when he was only wearing a yellow collared shirt in all previous shots. (00:05:05 - 00:05:48)
Continuity mistake: When Cyclops and Jean are approaching the newspaper kiosk, its opening is facing the sidewalk. When the shot changes to them walking past it, the opening has been replaced by a wall with newspaper clippings and a painting on it. Moments later, they are approaching the same kiosk, after he tells her that his mind is on nothing but her. (00:05:13)
Continuity mistake: After Jean and Cyclops first kiss after she tells him to relax a little, his left arm is around her shoulder and it suddenly jump cuts to his side with his hand in his pocket. (00:05:37)
Continuity mistake: When Leech steps in front of Cyclops and Jean to steal fruit from the vendor, you can see the street behind him. When the shot changes, there is suddenly what appears to be a covered bus stop behind him. (00:05:48)
Continuity mistake: When Leech begins to telekinetically steal fruit from the vendor cart, he is stealing a red apple and what appears to be an orange with a yellow peel. When the shot changes, the orange is now orange in color, and as the two pieces of fruit move towards Leech, the orange is on his right, and the apple on his left. When the shot changes, the orange is now yellow in color again, and the fruits have swapped sides. (00:05:52)
Continuity mistake: When Leech telekinetically splits up the mob, on his left are a man with a light blue shirt, followed by a man with an orange shirt, and man with a light blue shirt behind him. On his right are a man with a green jacket and yellow shirt, a man with an orange jacket and pink shirt behind him, and lastly, a man with a blue jacket and yellow shirt. When the shot changes, the men have not only swapped sides, but now it is two men in light blue shirts in front of the man in the orange shirt, and the man with the orange jacket and pink shirt is now just wearing an orange shirt, and he is standing in front of the man with the green jacket and yellow shirt, and the man with the blue jacket and yellow shirt is in front of him. (00:06:05)
Continuity mistake: When the mob was first chasing Leech, it was six men. When they have reached the subway platform, it is now four completely different men and one woman. (00:06:05 - 00:06:28)
Continuity mistake: When Tar Baby traps the mob inside the subway platform, he seals off the stairs with a wall of tar. When Cyclops and Jean have arrived to intervene, the wall of tar is now in front of the turnstiles. (00:06:24)
Continuity mistake: The picture of Jean and Cyclops Wolverine has framed shows them against a yellow-orange background, and Cyclops' sunglasses are red. When the picture is shown again at the end of the episode, the background is now white and Cyclops' sunglasses are gray. (00:08:14 - 00:20:44)
Audio problem: When Callisto says to Cyclops "away from those who fear us," her mouth is completely closed. (00:09:20)
Deliberate mistake: The video footage Callisto has of the X-Men battling Sentinels at the Mutant Registration Center is just clips from that episode. (00:09:27)
Other mistake: When Xavier is in the War Room with the rest of the team showing where the closest he could pinpoint Cyclops and Jean's location is, he is sitting in one of the chairs positioned around the table. Xavier is paraplegic and usually sits in his own hover chair. While there's no reason he couldn't be sitting in a regular chair, it would be very impractical for him to do so, especially if he's just instructing his team where they need to go. (00:11:07)
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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