Other mistake: When Gambit is consoling Rogue just before she is taken to be tortured, he tells her that he loves her, and states that he has never said that to anyone before. But as we learned earlier in the season, Gambit was engaged in his youth to Bella Donna. Surely he told her he loved her at some point. Rogue is aware of this aspect of Gambit's past, so he would have nothing to gain by lying to her about it.
Plot hole: After Beast and Dr. Bohlson leave Carly's room, they briefly chat in the hallway just outside the door for less than 15 seconds in real time, and then discover that in that brief time frame, the Friends of Humanity abducted Carly from her second-story room via the window, managed to incapacitate the nurse, security guard and Carly's father, toss around furniture and spray paint "For Humanity" on one of the walls, all without any of the victims making a sound or the Friends of Humanity making a sound themselves. The Friends of Humanity aren't ninjas, rather they are shown to be somewhat bumbling, so there's no way they could have done all that as quickly and quietly as shown. (00:12:30)
The Dark Phoenix (3): The Dark Phoenix - S3-E13
Continuity mistake: When the Shi'ar beam down in front of the X-Men, Lilandra and Gladiator have a gap of a few feet between them. When the shot changes, they are suddenly standing closer together. (00:19:14)
The Dark Phoenix (2): The Inner Circle - S3-E12
Continuity mistake: When Sebastian Shaw is escorting Jean out of the room, there is a chair with a side table in the foreground. A couple of shots later when Wyngarde is sitting in the chair, the side table has disappeared. (00:06:09)
The Dark Phoenix (4): The Fate of the Phoenix - S3-E14
Audio problem: When Lilandra's advisor is saying "The X-Men face hopeless odds," his mouth is closed for the word "face." (00:08:57)
The Dark Phoenix (4): The Fate of the Phoenix - S3-E14
Continuity mistake: When Xavier is explaining that he challenged the Shi'ar to a duel of honor, there is no-one standing between him and Lilandra, Earthquake, and Gladiator. When the shot changes, Gambit and Beast are now standing between them. (00:02:24)
The Dark Phoenix (2): The Inner Circle - S3-E12
Continuity mistake: When the Dark Phoenix has broken Wyngarde's illusion, and he collapses to his knees, his hairtie has gone from being a blue band to a black bow tie. (00:19:15)
Dark Phoenix (1): Dazzled - S3-E11
Continuity mistake: When Wyngarde first invades Jean's dream and places her down on the bed, she has a mole near her left nostril. Later in the scene when she is looking overboard, the mole is next to the corner of her lips, and even briefly disappears from her face. (00:13:35 - 00:14:23)
Dark Phoenix (1): Dazzled - S3-E11
Continuity mistake: When Sebastian Shaw is asking if the Phoenix destroyed herself, Wyngarde is standing to Shaw's right. When the shot changes, Wyngarde is standing behind the White Queen, directly across from Shaw. (00:07:56)
The Dark Phoenix (4): The Fate of the Phoenix - S3-E14
Continuity mistake: When Lilandra slams her first down onto the control panel, the appearance of the control panel changes between shots. (00:17:14)
The Dark Phoenix (4): The Fate of the Phoenix - S3-E14
Continuity mistake: When Cyclops and Jean are hiding in the shallow alcove, as he is saying there's so much he wants to say to her, his teeth alternate between being white and flesh-colored. (00:13:56)
The Dark Phoenix (4): The Fate of the Phoenix - S3-E14
Continuity mistake: When Lilandra is explaining that it is her duty to protect her people, the band around her elbow alternates between being gray and yellow. (00:06:18)
The Dark Phoenix (4): The Fate of the Phoenix - S3-E14
Continuity mistake: When Cyclops asks Lilandra why she has kidnapped the X-Men, the background shows several sections of people in stadium seating, several yards in the distance. When the shot changes, the background now shows a wall that is very close to her head. (00:03:02)
The Dark Phoenix (4): The Fate of the Phoenix - S3-E14
Continuity mistake: When Storm is questioning why the Shi'ar Imperial Guard have stopped approaching the X-Men, Gambit's pants are colored blue, when they should be black. (00:02:16)
The Dark Phoenix (4): The Fate of the Phoenix - S3-E14
Revealing mistake: When Xavier is invading Lilandra's mind, the ball of psychic energy on her head shifts left and right as the camera zooms in, likely indicating a composite shot. (00:02:07)
The Dark Phoenix (4): The Fate of the Phoenix - S3-E14
Continuity mistake: When Wolverine says "You got that right," there is no-one standing between him and Xavier and Rogue. When the shot changes, Storm is now standing between the three aforementioned characters. (00:02:03)
The Dark Phoenix (2): The Inner Circle - S3-E12
Continuity mistake: When Wolverine emerges from the dumb waiter and kicks the waiter against the wall, the waiter ends up beneath a painting. When Wolverine walks toward the turkey, you can see the painting on the wall, but the waiter has disappeared from beneath it. (00:07:24)
The Dark Phoenix (2): The Inner Circle - S3-E12
Continuity mistake: When the White Queen is telling Shaw and Wyngarde to think, there is a painting on the wall to Shaw's left. When the shot changes, the painting has disappeared. (00:06:28)
Dark Phoenix (1): Dazzled - S3-E11
Continuity mistake: When Wolverine slashes at Donald Pierce's arm, the sleeve of Pierce's jacket is torn around the elbow. When the shot changes, nearly the entire sleeve is torn off. (00:19:27)
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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