Continuity mistake: When Magneto is saying "Mutants will come to me by the thousands," he raises his right fist up near his face. He then begins lowering his hand, and when the shot changes, it is instantly down at his side. (00:20:29)
Continuity mistake: When Xavier is saying "We cannot afford to lose again," his fist is raised, and Storm is leaning over him. When the shot changes, his hand is resting on his hoverchair, and she is standing upright and further away from him. (00:20:05)
Continuity mistake: When Storm is saying "We failed, Professor, together," her lips are red. When the shot changes, her lips are brown. (00:20:00)
Continuity mistake: When Magneto topples Xavier out of his hoverchair, there are two white rectangles on the hoverchair that briefly turn yellow. (00:12:11)
Continuity mistake: After Wolverine says "Let's go kick his butt," he turns his head and you can see his ear changes color from white to the same color as the rest of his flesh. (00:04:15)
Continuity mistake: When Xavier says "Homo superior," his left hand is raised. When the shot changes, his hands are clasped together on the desk in front of him. When the shot changes again to over his shoulder, his hands are nowhere to be seen. (00:03:58)
Continuity mistake: When Xavier says Magneto believes mutants are the next stage in human evolution, the gray nameplate on his desk is centered. When the shot changes, it is now colored brown and has shifted to Xavier's right, near the computer monitor. Additionally, a folder appears on the desk between shots. (00:04:01)
Continuity mistake: When Jubilee raises Sabretooth's arm restraint, the interior side of it is shown to extend all the way down to the arm rest. When the shot changes, it now has an opening for a person to move their arm through. (00:15:31)
Continuity mistake: When Sabretooth is trying to force Wolverine's claws into his own face, they are next to a set of steps. When the shot changes, there are no steps anywhere near them. (00:18:46)
Continuity mistake: When Sabretooth is trying to force Wolverine's claws into his own face, the black part of Wolverine's mask on either cheek is incorrectly colored yellow. (00:18:13)
Continuity mistake: Numerous episodes depict the War Room as being a circular room completely enclosed from the rest of the underground facilities. However, when Wolverine is confronting Sabretooth in the War Room, it is a wide open area with numerous corridors. (00:16:23 - 00:17:05)
Continuity mistake: When Sabretooth is watching Senator Kelly's press conference, his chair is directly facing the TV. After Jubilee turns off the TV and walks towards Sabretooth, his chair has now rotated roughly 90° clockwise. (00:14:47)
Continuity mistake: When Senator Kelly is giving a press conference to declare his candidacy for President, at the start there is a flag immediately to his right. When the shot changes, after a few seconds the camera pans out and the flag has now moved several more feet to his right. (00:14:05)
Continuity mistake: When Rogue is blindly searching for Cyclops, the black circle with the red X on her chest is now a red circle with a yellow X. (00:11:14)
Continuity mistake: When Jubilee blasts Sabretooth through walls of the War Room and outside, it is shown to be on the mansion's ground level. Many other episodes however depict the War Room to be in the underground levels of the mansion, specifically in the episode "The Unstoppable Juggernaut" where the War Room is still intact after the mansion is destroyed from the ground up.
Continuity mistake: When Sabretooth tells Jubilee that her powers are useless if she can't use her hands, the glove on her left hand turns from yellow to brown multiple times. (00:15:50)
Continuity mistake: When Sabretooth is sitting in the hover chair in the War Room, the chair is shown to be hovering up and down in the wide shot, but when a closeup of Sabretooth is shown, the background behind him remains stationary, indicating the chair is also stationary. (00:04:35)
Continuity mistake: When Wolverine says to Sabretooth "Be careful what you ask for," his arms are yellow. (00:17:05)
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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