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)
Night of the Sentinels: Part 2 - S1-E2
Continuity mistake: When Gyrich both enters and exits the White House exercise room, the file folder under his arm is the size of a briefcase. When he angrily throws the folder, it is now the standard file folder size. (00:14:45 - 00:15:17)
Night of the Sentinels: Part 1 - S1-E1
Continuity mistake: When Beast tosses Wolverine over the fence, Wolverine's bare arms are the same yellow color as his costume. (00:19:12)
Night of the Sentinels: Part 1 - S1-E1
Continuity mistake: When the arcade manager is confronting Jubilee after she accidentally destroyed the game she was playing, he is several feet away from her, with other patrons between them. When the shot changes, he is suddenly in her face. (00:03:27)
Night of the Sentinels: Part 2 - S1-E2
Continuity mistake: When Gyrich is telling Jubilee that he wants to ask her about the mutants that helped her at the mall, the microphone is up to his mouth. When the shot changes to him tapping his right index finger on the desk, the microphone is nowhere near his mouth. (00:04:27)
The Unstoppable Juggernaut - S1-E8
Continuity mistake: When Juggernaut is stealing the stacks of cash from the bank vault, the money is more yellow in color. When Wolverine slashes open the bags and the cash spills out, the money is now green. (00:12:29 - 00:13:52)
Night of the Sentinels: Part 1 - S1-E1
Continuity mistake: When the guard orders Wolverine, Beast and Morph to halt, Wolverine and Morph are standing next to each other, with Beast behind and between them. When the shot changes, Morph is now behind Wolverine to his left, and Beast is behind Morph and to his left. (00:19:19)
Continuity mistake: When Magneto drops Wolverine, Storm and Cyclops onto the ground, Wolverine and Cyclops are lying mostly perpendicular to Storm. When it changes to a shot of them getting up, they are all parallel to each other. (00:17:18)
Continuity mistake: The prosecutor for Beast's trial is wearing a pink suit. When the unruly civilian is being escorted out of the courtroom, in a wide shot, the prosecutor's suit is now white. (00:08:29 - 00:10:22)
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 the X-Men discover Jean and Annalee in the small room, neither Jean or Annalee are casting shadows on the wall behind them. When the shot changes, their shadows are now on the wall. (00:12:37)
The Unstoppable Juggernaut - S1-E8
Continuity mistake: When Rogue and Storm first enter the jail, the desk clerk is wearing a blue shirt. When Rogue begins to flirt with him, his shirt is now white. (00:09:48)
Continuity mistake: When Wolverine is slashing at Callisto's staff, it is light purple. When he completely shreds a center portion of it, that portion is blue, and when the shot changes, the rest of the staff is red. Additionally, the center section of the staff has reduced in length after Wolverine shreds it. (00:14:35 - 00:15:03)
Continuity mistake: When Storm and Callisto are about to engage in combat, they are using staves that look like lightsabers, with the hilts at the bottom. When they start striking at each other, both staves now resemble a double-edged lightsaber, with the hilt in the middle. (00:18:25)
Continuity mistake: When Xavier is talking to Jean and Cyclops at the end, the three of them, along with Storm, are all to the left of the bed Gambit is lying on, with Storm being behind Xavier, over his right shoulder, and a piece of machinery behind her. When the shot changes, it is a closeup of Xavier, and neither Storm, nor the machinery are visible over Xavier's shoulder. When Jean and Cyclops leave the room, Xavier is now at the foot of Gambit's bed, several feet away from Storm. (00:20:08 - 00:20:32)
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 Xavier is using Cerebro to look for Magneto, his blue and black tie turns yellow when Jubilee says "Professor?" When Storm says "Charles, are you all right?", it is back to being blue and black, and the blue stripes turn yellow before our eyes. (00:11:41)
Night of the Sentinels: Part 2 - S1-E2
Continuity mistake: When Beast is leaping through the corridor, the black X with the black rectangular border on a red background on his waistband briefly becomes a red rectangle on a yellow background with no X. (00:02:37)
Continuity mistake: When the statue is about to fall on Wolverine, his arms are colored yellow. (00:16:25)
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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