One Man's Worth: Part 2 - S4-E2
Revealing mistake: Bantam's irises turn completely white for a split-second when he is watching Fitzroy's recording. (00:17:35)
Revealing mistake: When Moira gets up from her seat to check on Xavier, her left leg passes through the left armrest. (00:14:45)
Revealing mistake: When Proteus is leaving his father's home while possessing the police officer, the green glow of his eyes doesn't stay in place as he is moving. You can see the green glows leave his face and float in midair with the eye slots on the face turning black. It appears that the animators couldn't keep the glowing eyes synchronized with the body movement. (00:07:30)
Beyond Good and Evil: Part 1 - S4-E8
Revealing mistake: The slice of cake that Wolverine cuts out already has the cut-lines animated on it before he starts slicing it. Probably to make it easier for the animators to animate his hand movement. (00:11:05)
Beyond Good and Evil: Part 1 - S4-E8
Revealing mistake: When Mr. Sinister is mocking Jubilee, take a close look at his neckline as he moves his head. The animators moved his neckline as he moved his head, but his shoulders stay in place, so his head and neck look like they are floating above his shoulders. (00:15:30)
Beyond Good and Evil: Part 2 - S4-E9
Revealing mistake: When Psylocke is scaling the cliffs, her left leg passes through the cliff walls. (00:09:20)
Beyond Good and Evil: Part 4 - S4-E11
Revealing mistake: After the horsemen collect the orb from Apocalypse, a second "onion skin" head of Apocalypse appears. (00:11:45)
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)
Revealing mistake: When Rogue's phone is ringing you can see that the phone is halfway absorbed into her mirror. (00:04:15)
Revealing mistake: Wolverine's nipples literally disappear from his chest when he says "Do I feel lousy." (00:07:15)
Secrets, Not Long Buried - S4-E15
Revealing mistake: Instead of staying in place, the energy surging around Watchdog's head moves down the screen as the camera pans down. (00:02:35)
Secrets, Not Long Buried - S4-E15
Revealing mistake: When the Lady Gardener shuts her door on Cyclops, his right arm stays inside her house in front of the door frame. (00:14:35)
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)
Family Ties - S4-E17
Revealing mistake: When Quicksilver is fidgeting inside his containment shell, the animators neglected to properly sync his body movement. You can see that his shoulders are not "connected" to his arms, as if his head and shoulders were separated from the rest of his body. (00:16:00)
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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