Revealing mistake: When Morph is saying "You never were very bright," part of his shirt collar has been drawn on his chin. (00:07:20)
Revealing mistake: When Warren's girlfriend is looking for him in his lab, she is startled by Cable who is hiding behind the door and slams it shut once she enters the room. When she is startled and looks back at Cable, the animation is not very fluid. As she is turning around to look at Cable, her "onion skin" form remains, making it look like there are two of her. (00:03:35)
Slave Island - S1-E7
Revealing mistake: When Storm is saying "There will be thousands of them," her mouth briefly disappears from her face. (00:16:45)
Slave Island - S1-E7
Revealing mistake: When Gyrich walks forward to shake the Leader's hand, the ground beneath them is noticeably shaking, possibly indicating a composite shot. (00:10:35)
Revealing mistake: When the assassin is handing Bobby the tithe box, the assassin's left hand passes through the chair Bobby was sitting in. (00:11:15)
Revealing mistake: In the opening shot of the Washington Monument, the monument is very noticeably shaking left and right as the camera pans up (likely indicating that the monument and the background are a composite image). (00:01:00)
No Mutant Is an Island - S5-E4
Revealing mistake: When Killgrave is saying "On your knees," his eyes jump off his face. (00:18:45)
No Mutant Is an Island - S5-E4
Revealing mistake: When Rusty is being brainwashed, his eyes move down his cheeks as his head nods. (00:10:55)
No Mutant Is an Island - S5-E4
Revealing mistake: When Sarah turns off the stove burner you can see that there is an outline of a knob that the animators either forgot to fill in or forgot to erase. (00:05:35)
Revealing mistake: When Rogue is shown tearing off the first portion of the submarine's hull, her feet are missing. (00:17:55)
The Phalanx Covenant: Part 2 - S5-E2
Revealing mistake: When Forge says "That's where we'll begin our assault," his mustache disappears from his face. (00:14:50)
The Phalanx Covenant: Part 2 - S5-E2
Revealing mistake: The shot of Cameron Hodge glaring at Xavier after Xavier asks him about his lack of humanity is a recycled shot from the previous episode. (00:14:30)
The Phalanx Covenant: Part 1 - S5-E1
Revealing mistake: When Beast lunges away from the Phalanx disguised as several people in hazmat suits, after he lands he glides across the grass. (00:08:15)
The Phalanx Covenant: Part 1 - S5-E1
Revealing mistake: The shot of police cars surrounding Sabretooth and him throwing one of them into the air is a recycled shot of the very first shot in the series from the season 1 episode "Night of the Sentinels, Part 1." It's even revealed a few minutes later in the episode that this isn't actually Sabretooth, but a Phalanx facsimile that has taken his form, which makes the fact that Sabretooth's actions are being recycled all the more dubious. (00:01:35)
Family Ties - S4-E17
Revealing mistake: After the New Men have captured Magneto, Wolverine, Scarlet Witch and Quicksilver, the establishing shot of the High Evolutionary's headquarters is a recycled shot of when Scarlet Witch and Quicksilver first arrived at his headquarters a few minutes earlier in the episode, played on a loop (note the lightning strikes and the High Evolutionary's pink energy field being repeated). (00:05:35 - 00:12:40)
Family Ties - S4-E17
Revealing mistake: When the High Evolutionary is asking Scarlet Witch and Quicksilver to place their arms in his DNA scanner, his mouth looks like it is jumping off his face as he is speaking. (00:06:35)
Revealing mistake: Wolverine's nipples literally disappear from his chest when he says "Do I feel lousy." (00:07:15)
The Lotus and the Steel - S4-E13
Revealing mistake: The footage of Jubilee flying off in the mini-jet is recycled footage of her flying Colossus back to Russia from the season 4 episode "Red Dawn." You can even make out Colossus' silhouette in the window over the passenger seat in one shot, even though Jubilee is supposed to be by herself. (00:07:35)
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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