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: 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: 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: 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 Moira is saying to Proteus "Kevin it's time to come home," you can see that Rogue is suddenly not wearing any lipstick. (00:04:05)
Continuity mistake: At the very end of the previous episode after Proteus had messed with Wolverine's sense of reality, Wolverine is shown whimpering in an open area. When Wolverine is shown at the beginning of this episode still whimpering, he has suddenly moved next to a treeline. Given the state of shock he was in, it's doubtful he would have gotten up and moved. (00:02:00)
Continuity mistake: After Joe hangs up on Moira, if you look at Wolverine in the background you will see that his face is colored yellow. (00:17:30)
Continuity mistake: When Proteus possesses the truck driver, the truck driver's wristwatch disappears in one shot. (00:15:10)
Continuity mistake: When Wolverine, Rogue and Beast are approaching Proteus in the Blackbird, in the first shot you can see through the windows that Wolverine is wearing a jacket. When the shot changes, the jacket is suddenly gone. (00:13:05)
Continuity mistake: During Xavier's flashback, Jean Grey goes from wearing her current (as of the show's broadcast) uniform while training in the Danger Room to her original "Marvel Girl" uniform when Amelia is leaving the mansion. Additionally, when Xavier is talking to Amelia in the Danger Room's control room, he is in his usual hoverchair, yet when Amelia is leaving the mansion, he is in a regular wheelchair. (00:05:25)
Continuity mistake: After Moira and Banshee are knocked back into the wall by Proteus, the amount of rubble around them changes between shots. (00:02:15)
One Man's Worth: Part 2 - S4-E2
Continuity mistake: When Fitzroy is draining energy from Xavier in order to create a time portal, he is completely surrounded by Bishop, Storm and Bantam. A few shots later there is no one standing around Fitzroy and Xavier. (00:18:35)
One Man's Worth: Part 2 - S4-E2
Continuity mistake: When the coffee shop owner is caught in Storm's whirlwind, his beard is flesh-colored. (00:03:35)
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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