Continuity mistake: The security footage of Cortez betraying Magneto is slightly different than the event itself. Cortez stated that Magneto would serve the mutant cause better as a martyr and then jettisoned his chambers into space. The security footage somehow has a shot of Magneto's chambers being jettisoned from a long distance with Cortez's martyr comment voiced over. (00:14:40)
Continuity mistake: After Carmella Unuscione releases Wolverine and Rogue from her psionic grasp, Wolverine's face is colored blue. (00:15:00)
Other mistake: When Cortez is using the remote control for the power inhibitor collar to fend off Gambit and cause him pain, you can see that Cortez is actually pushing the "Mutant Power On" button and not the "Pain" button that's just above it. (00:16:25)
Plot hole: This episode establishes that Magneto lost his family in the Holocaust, which is taken from the comics. However, the season 1 episode Enter Magneto established that Magneto lost his family when a guerilla army occupied his country.
Beyond Good and Evil: Part 1 - S4-E8
Continuity mistake: A giant stone is covering the secret door to Apocalypse's Lazarus Chamber. After Cable presses the snake lever to open the door, the giant stone has disappeared. (00:03:35)
Beyond Good and Evil: Part 1 - S4-E8
Continuity mistake: The cake frosting on Cyclops and Jean's faces goes from being to just around their mouths to all over their cheeks. (00:10:50)
Beyond Good and Evil: Part 1 - S4-E8
Revealing mistake: The slice of cake that Wolverine cuts out already has the cut-lines animated on it before he starts slicing it. Probably to make it easier for the animators to animate his hand movement. (00:11:05)
Beyond Good and Evil: Part 1 - S4-E8
Continuity mistake: The crowd of animated extras that are on the mansion's porch have suddenly disappeared when Jean and Cyclops get in their car. (00:11:35)
Beyond Good and Evil: Part 1 - S4-E8
Continuity mistake: When Hairbag knocks Wolverine down, Rogue can be seen lying on the ground next to Storm. A couple of shots later she is shown lying next to Gambit. (00:12:40)
Beyond Good and Evil: Part 1 - S4-E8
Revealing mistake: When Mr. Sinister is mocking Jubilee, take a close look at his neckline as he moves his head. The animators moved his neckline as he moved his head, but his shoulders stay in place, so his head and neck look like they are floating above his shoulders. (00:15:30)
Beyond Good and Evil: Part 1 - S4-E8
Plot hole: Gambit remarks that Shard is his kind of time traveler. However, Shard was inside the mansion and Gambit was outside when he said that, and he had never previously met her, so there was no way he could have known who she was without having even seen her or even that she was a time traveler. (00:17:20)
Beyond Good and Evil: Part 1 - S4-E8
Continuity mistake: Gambit and Beast have instantly appeared behind Wolverine after he asks how the Nasty Boys got inside the mansion. (00:17:55)
Beyond Good and Evil: Part 1 - S4-E8
Plot hole: Beast comments on Mr. Sinister's new-found time travel abilities. However, Beast has no way of knowing that Mr. Sinister is time traveling. He only knows that Mr. Sinister is using portals, which could just as well be for teleportation. (00:18:40)
Beyond Good and Evil: Part 2 - S4-E9
Continuity mistake: Deathbird's wings alternate between being red and purple after Apocalypse betrays her. (00:05:05)
Beyond Good and Evil: Part 2 - S4-E9
Audio problem: When Xavier says "Assemble the X-Men," his mouth movement is slightly out of sync. (00:05:55)
Beyond Good and Evil: Part 2 - S4-E9
Revealing mistake: When Psylocke is scaling the cliffs, her left leg passes through the cliff walls. (00:09:20)
Beyond Good and Evil: Part 2 - S4-E9
Continuity mistake: The length of the chain attached to the collar of Archangel's guard dog varies. When the dog is first shown, the chain is only shown to be around three feet long. When the dog discovers Psylocke, it is able to run several feet towards her and away from the wall where it was chained up. (00:09:35)
Beyond Good and Evil: Part 2 - S4-E9
Continuity mistake: When Psylocke renders Archangel's guard dog unconscious, his chain is still attached to his collar. When Archangel checks on the dog, the chain is missing. (00:09:50)
Beyond Good and Evil: Part 2 - S4-E9
Character mistake: Wolverine refers to Psylocke as having black hair and Archangel refers to her as being raven-haired. She has purple hair. (00:11:55)
Beyond Good and Evil: Part 2 - S4-E9
Continuity mistake: Sabretooth tears off a piece of Psylocke's clothing, yet there is no sign of any part of her clothing being torn afterwards. (00:14:45)
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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