Continuity mistake: When Trask turns the laser onto the propane gas tank, it is on Master Mold's left. When Master Mold reaches down to try and stop the laser before it causes the tank to explode, it is now on his right. (00:16:04)
Continuity mistake: When Cyclops is running through the mine to search for Wolverine and Gambit, he uses his visor to track their location. When the shot changes to a first person view through Cyclops' visor, the background is merely moving up and down. If he was running as the previous shot had shown, the objects in the background from his point of view would become larger as he got closer to them. (00:16:50)
Continuity mistake: When Rogue is calling out to Gambit just before Jean and Senator Kelly exit the mine shaft, the X logo on her chest is a yellow X on a red background, when it should be a black X on a red background. (00:17:57)
Revealing mistake: When Xavier is parachuting towards the ground, the stars in the sky are flickering on and off. (00:19:00)
Factual error: When a parachuting Xavier is about to land, you can see his legs are bent at the knee to brace for landing. Since Xavier is a paraplegic, he shouldn't be able to do this. (00:19:14)
Continuity mistake: At the beginning of Senator Kelly's campaign speech, his campaign button is predominantly white with some blue at the top and bottom. When the shot changes, the majority of the button is now blue, with only a small portion in the center being white. (00:19:20)
Factual error: When Senator Kelly is giving his campaign speech, the U.S. flag behind him is missing one stripe and has at least two too many stars. (00:19:30)
Continuity mistake: When Beast is first shown in his prison cell, the X logo on his waistband is black with a red background. When Jubilee hugs him, it is now a red x on a yellow background. (00:19:51)
Plot hole: Magneto states that he went to Washington, DC to witness Senator Kelly's assassination. But Magneto had no way of knowing about the assassination plot. Mystique was the one who was attempting to assassinate Kelly, and Apocalypse was the one who carried out the order. At this point in the show, Magneto had not worked with either Mystique or Apocalypse, and it's highly doubtful that Mystique would leak the plot, since it was supposed to be covert.
Continuity mistake: Magneto reveals to Senator Kelly that he went to Washington, DC to personally witness his assassination. The flashback to the previous episode reveals that Magneto was watching Mystique (masquerading as Gambit) attempt to assassinate Kelly and the real Gambit's intervention through a window. Magneto can be seen as plain as day watching in the window in the flashback, yet in the actual episode, Magneto is never there. The design of the window is also different, as well as the color of the curtains. The room itself also appears to be smaller in the flashback.
'Til Death Do Us Part: Part 1 - S2-E1
Continuity mistake: When Wolverine leaps out to engage the Danger Room doppelganger of Cyclops, his claws are extended. When he lands, there is a closeup shot of his right hand, and his claws are suddenly retracted, and he extends them again. (00:02:16)
'Til Death Do Us Part: Part 1 - S2-E1
Continuity mistake: When Wolverine stabs the Danger Room doppelganger of Cyclops, he is running him through in the center of the chest. When the shot changes, he is now stabbing him through the left collar bone area. (00:03:04)
'Til Death Do Us Part: Part 1 - S2-E1
Other mistake: When Gambit is attempting to kiss Rogue at the wedding, the man standing over Gambit's right shoulder has no face. (00:04:03)
'Til Death Do Us Part: Part 1 - S2-E1
Other mistake: When Morph, disguised as the reverend, is saying goodbye to Cyclops, the characters in the background never move a muscle. (00:04:10)
'Til Death Do Us Part: Part 1 - S2-E1
Continuity mistake: The ribbon on the wedding present that Beast is carrying disappears when Jean's bouquet lands on it. (00:05:30)
'Til Death Do Us Part: Part 1 - S2-E1
Continuity mistake: When Beast is saying "What's in a name," he and Cyclops are standing on the right side of the red carpet, and Gambit is standing right behind Beast. A couple of shots later, Beast and Cyclops are now standing on the left side of the red carpet, and Gambit is now standing several feet away by the door. (00:05:32)
'Til Death Do Us Part: Part 1 - S2-E1
Plot hole: The establishing shot of the White House indicates that President Kelly's press conference is taking place there. A member of the Friends of Humanity disguised as a mutant busts into the room and starts terrorizing the reporters and destroying everything. The Secret Service would have either detained or shot this man long before he could have even gotten close to the press conference. Graydon Creed also shoves a security guard that tries to intervene but somehow isn't arrested for it. (00:05:50 - 00:06:35)
'Til Death Do Us Part: Part 1 - S2-E1
Continuity mistake: Professor X's wedding tuxedo suddenly changes into his usual green suit when Beast is giving an update about President Kelly. (00:05:50)
'Til Death Do Us Part: Part 1 - S2-E1
Continuity mistake: When President Kelly is issuing a pardon to Beast, the lapels of his suit jacket are white. A couple of shots later, they are the same peach color as the rest of the jacket. (00:05:54)
'Til Death Do Us Part: Part 1 - S2-E1
Continuity mistake: When Morph is first blasted by the Sentinels in the flashback, it leaves a small hole in the chest area of his uniform. When Mr. Sinister approaches him, the hole is now much larger, exposing his entire chest and abdomen. (00:07:47)
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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