No Mutant Is an Island - S5-E4
Continuity mistake: When Cyclops first approaches the orphanage there is a tricycle on the porch near the edge of the steps. When Sarah comes out and greets him, the tricycle has disappeared. (00:04:35 - 00:05:10)
No Mutant Is an Island - S5-E4
Continuity mistake: When Cyclops throws his uniform on the ground, it turns into a dark gray color and the yellow paraphernalia attached to it disappears. (00:03:40)
No Mutant Is an Island - S5-E4
Continuity mistake: When Jubilee starts crying, Gambit's normally-black pants are colored blue. (00:01:50)
No Mutant Is an Island - S5-E4
Continuity mistake: When the X-Men are sitting in a circle at the beginning, Cyclops' gloves are missing above the wrist. (00:01:10)
No Mutant Is an Island - S5-E4
Continuity mistake: The hedge wall-enclosed landscaped area in front of the mansion at the beginning of this episode is an open lawn with trees and bushes in all other episodes. (00:01:05)
Continuity mistake: When the X-mansion is shown at the end of the episode, the landscaping around it is different than what was shown early in the episode. When the mansion was first shown, there is a shrub in the shape of a circle on the lawn across from the mansion, but at the end of the episode, the circle-shaped shrub has turned into some bushes. The bushes and trees around the mansion are also different looking and at the far side of the mansion the shrubs have grown taller. Additionally, when Wolverine is walking away from the mansion at the end, a hedge-wall has appeared next to the mansion. It's actually common for the landscaping outside the mansion to vary drastically from episode to episode. This is the first time I noticed it changing within the same episode. (00:04:25 - 00:19:25)
Continuity mistake: When Rogue and Beast are in the Blackbird hovering above Omega Red in the ocean, the sky varies from being midday to being twilight depending on the scene.
Continuity mistake: The red omega symbols on the back of Omega Red's hands disappear and reappear throughout the episode, and are even sometimes colored white.
Continuity mistake: When Omega Red is wrapping the metal around the Storm, the portion of the metal that is protruding from Omega Red's grasp alternates between being brown and white in the same shot. (00:16:30)
Continuity mistake: When Beast presses the button to listen in on Omega Red, Storm and Wolverine, Rogue's arm is flesh-colored whereas it should be green since she is wearing her uniform. (00:13:35)
Continuity mistake: The mini-sub that Storm docked onto the hull of the nuclear submarine disappears and reappears throughout the rest of the episode. (00:07:20 - 00:17:45)
Continuity mistake: When Storm says to Wolverine "You know small spaces overwhelm me," you can see that her lightning bolt earrings are suddenly missing. (00:06:30)
Continuity mistake: The number of "rows" on the purple devices on Omega Red's face varies throughout the episode, sometimes even changing quantity in the same shot.
Continuity mistake: When Wolverine says "Who do these genius spy-catchers think they're dealing with, Winnie the Pooh?!" his tongue is flesh-colored instead of being a normal reddish hue. (00:04:30)
Continuity mistake: When Wolverine says "For a boy scout! Omega Red eats the stuff for breakfast!" his normally-red belt is yellow, goes back to being red a couple of shots later, and then is yellow again a couple of shots after that. (00:04:45)
Continuity mistake: When the colonel is talking to Omega Red on the giant monitor, he is standing in different spots throughout the scene depending on the shot. (00:02:45 - 00:04:10)
Continuity mistake: When Omega Red was frozen at the end of the season 2 episode "Red Dawn", his mouth was open. When the military discovers him at the beginning of this episode, his mouth is closed. (00:02:30)
The Phalanx Covenant: Part 2 - S5-E2
Continuity mistake: The final shot of the episode shows Jubilee among the group of X-Men. However, she was not present in the group shots that preceded this one. (00:20:40)
The Phalanx Covenant: Part 2 - S5-E2
Continuity mistake: When the group is standing together in a circle at the end, Xavier is sort of in the center of the circle and Rogue and Storm are several feet to his right. When the shot changes, Rogue and Storm are suddenly right next to Xavier. (00:19:25)
The Phalanx Covenant: Part 2 - S5-E2
Continuity mistake: When Jean Grey hugs Cyclops, her hands are colored blue. (00:19:25)
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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