Continuity mistake: When Xavier is speaking to Proteus telepathically, the position of his shirt and jacket sleeves go from being a few inches below his wrist in one shot, and then just slightly under his wrist in the next. (00:12:55)
Continuity mistake: When Proteus leaves the town hall, the door he exits is shown to lead into an alleyway. Moments later when Moira exits through the same door, it is shown to be leading into a corridor in the same building. (00:13:15)
Continuity mistake: The exit door and stairwell outside of the town hall are shown to be at the very edge of the building when Proteus goes through it. When Xavier, Beast, Rogue and Wolverine use the same door and stairwell, the building suddenly stretches on for several more feet. (00:13:20 - 00:13:55)
Continuity mistake: After Magneto crashes through the roof of the U.N. building, the nameplates designating the nations of the delegates have suddenly become blank. (00:02:20)
Continuity mistake: When Magneto forces the Genoshan delegate to sit down, the chairs surrounding him are empty. A couple of shots later, the chairs are occupied. (00:02:35)
Continuity mistake: When Magneto is showing Asteroid M to the delegates at the U.N. meeting, the Genoshan delegate he forced to sit down has either moved to another seat entirely or the people that were sitting around him moved to different seats and other people filled in their seats. (00:04:05)
Continuity mistake: When Gambit is trying to distract the Sentinels, both of his gloves are entirely fingerless whereas normally his gloves are only fingerless for the thumb, index and pinky fingers. (00:12:00)
Continuity mistake: A crowd of people has suddenly gathered in front of Magneto when Xavier says he wishes to speak with him. (00:14:20)
Continuity mistake: When Magneto first notices the missiles being fired at Asteroid M, he is dressed in loungewear and Xavier is wearing his usual green suit. When the shot changes Magneto is suddenly wearing his costume and Xavier is wearing a more casual outfit. Given how fast the missiles are shown to be approaching, they wouldn't have had time to change their clothes. (00:15:45)
Continuity mistake: The missiles that are fired at Asteroid M are first shown to be approaching from Earth. When the shot changes, they are coming from the opposite direction. When the shot changes again, they are once again approaching from Earth. (00:15:45)
Continuity mistake: When Rogue is asking about Gambit's whereabouts, she along with Beast and Xavier are close to the front of the shuttle. When the shot changes, the three of them as well as one of the astronauts are suddenly further back in the shuttle (note the doorway). (00:04:25)
Continuity mistake: When Fabian Cortez is scapegoating Gambit in front of the mob, he grabs him by the blue clothing that lines the body armor on his chest. When he says to Gambit "Mark my words X-Man..." the blue clothing is now the same brown color as Gambit's trenchcoat. (00:05:20)
Continuity mistake: In the flashback during Magneto's memorial, when the Nazis are approaching his home it says "Lehnsherr" on the door. After they kick the door open, the writing on the door has disappeared and either a hatch or a small window has appeared on the door from nowhere. (00:06:20)
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)
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
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
Continuity mistake: Gambit and Beast have instantly appeared behind Wolverine after he asks how the Nasty Boys got inside the mansion. (00:17:55)
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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