One Man's Worth: Part 1 - S4-E1
Character mistake: When the civilians are fleeing the coffee shop, there are two spelling errors on the coffee shop's marquee. Firstly, the name of the coffee shop is Rip Van Winkle, but on the marquee, Winkle is spelled as "Winkile." To the right of that, Coffee House is spelled as "Coffe House." (00:16:55)
Have Yourself a Morlock Little Christmas - S4-E12
Other mistake: When Gambit is tasting the food in the crock pot, his left arm has been drawn backwards.
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)
Secrets, Not Long Buried - S4-E15
Plot hole: At the speed Cyclops is traveling in his mini-jet when he passes Watchdog's tower, he would have been long out of range before Watchdog could force him out of the air into a crash landing, considering that Watchdog had to take time to alert Solarr of Cyclops' presence and be ordered to knock him out of the air. (00:02:30)
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)
Other mistake: The tail that Rogue grows appears out of thin air as if it were magic. Given that she's going through an organic transformation, the tail should have formed gradually out of her coccyx. (00:15:55)
Revealing mistake: When Rogue's phone is ringing you can see that the phone is halfway absorbed into her mirror. (00:04:15)
The Lotus and the Steel - S4-E13
Factual error: When Wolverine tears off the man's car door, he does so by putting his hands inside the spaces between the car door and the car's body. Those spaces are way too narrow for a person to fit their fingers inside. (00:03:25)
Have Yourself a Morlock Little Christmas - S4-E12
Other mistake: Rogue states that this is Jubilee's first Christmas as an X-Man. However, Jubilee was already a member of the X-Men when Senator Kelly declared his candidacy for President in season 1, and the season 2 premiere episode showed him being sworn-in as President. Election Day is in November and the President is sworn-in in January, so Jubilee should have already had at least one Christmas as a member of the X-Men. (00:02:00)
Beyond Good and Evil: Part 1 - S4-E8
Plot hole: Beast comments on Mr. Sinister's new-found time travel abilities. However, Beast has no way of knowing that Mr. Sinister is time traveling. He only knows that Mr. Sinister is using portals, which could just as well be for teleportation. (00:18:40)
Beyond Good and Evil: Part 1 - S4-E8
Plot hole: Gambit remarks that Shard is his kind of time traveler. However, Shard was inside the mansion and Gambit was outside when he said that, and he had never previously met her, so there was no way he could have known who she was without having even seen her or even that she was a time traveler. (00:17:20)
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)
Factual error: When Rogue attempts to correct the space shuttle's flight path, she has to let go because of the intense heat due to re-entry. Indeed, a temperature as hot as a shuttle in re-entry (upwards of 3,000° F) would have completely melted through her gloves, yet when she lets go, they only have a little smoke coming off them. (00:03:40)
Factual error: The Moon is more than 230,000 miles away from Earth, yet in a shot of Asteroid M just outside of Earth's orbit, the Moon is right there as well. (00:15:50)
Plot hole: Some of the footage Magneto is showing the delegates at the U.N. meeting includes footage Magneto could not possibly have had access to even if such footage existed, such as the X-Men having mission briefings in the War Room, the Morlocks living in the sewers or Warren Worthington emerging from being buried under several feet of snow at his secluded home in the mountains. (00:03:10 - 00:04:05)
Factual error: When Moira is calling her ex-husband Joe in Edinburgh from the Blackbird phone, she dials a typical U.S. seven-digit phone number (it looks like she dials 555-1238). However, even assuming she wouldn't be required to dial an exit code from the Blackbird, a typical Edinburgh phone number would have more digits, along the lines of +44-131-XXX-XXXX. (00:16:50)
Plot hole: This episode establishes that Magneto lost his family in the Holocaust, which is taken from the comics. However, the season 1 episode Enter Magneto established that Magneto lost his family when a guerilla army occupied his country.
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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