Days of Future Past: Part 2 - S1-E12
Revealing mistake: When Gambit draws a card from his sleeve to use as a trap, the gloved part of his hand that is below the pocket is translucent. (00:09:28)
Revealing mistake: When Jubilee is saying "What's anybody waiting for," her arm passes through Wolverine's body. (00:10:40)
Revealing mistake: When Xavier is parachuting towards the ground, the stars in the sky are flickering on and off. (00:19:00)
Days of Future Past: Part 1 - S1-E11
Revealing mistake: When Bishop is stepping out of the alley, you can see that he actually appears out of thin air and proceeds to step out from the outer wall of the building on the right. (00:10:15)
Revealing mistake: When Wolverine is skiing towards the land bridge, his whole body moves back several feet as the camera is panning right. (00:02:54)
Revealing mistake: When Gambit and Wolverine are pinned to the wall by Tar Baby, Gambit's face somehow gets between the tar and his right shoulder when he is saying "Sticky situation, mon ami." (00:12:01)
Night of the Sentinels: Part 1 - S1-E1
Revealing mistake: When the Sentinel is landing on the sidewalk, you can see the sidewalk is destroyed a split-second before the Sentinel's feet touch the ground. (00:02:05)
Revealing mistake: When the lab workers are running out of the plant as Magneto is wondering what Xavier looks like after so long, you can see the man in the lab coat and hard hat jerks backwards as he is near the flames. (00:07:53)
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 Wolverine, Storm, Rogue and Gambit are walking down the stairs to the subway station, you can see that they aren't actually descending the steps, but walking on thin air. (00:11:10)
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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