Revealing mistake: When Bella Donna is preparing to shoot a blast of energy at Rogue, her body passes through the left hand of the man on her left that was holding her back. Half of her cloak then disappears as she strides forward. (00:14:42)
Continuity mistake: When Bella Donna is saying the Assassins are prepared for the tithe, a man with long green hair is behind her on her left. When the shot changes, he appears to be standing between her and Gambit. When the shot changes again and Bella Donna is stroking Gambit's hair, he is nowhere to be seen. (00:14:16)
Continuity mistake: When Bobby and Pierre enter the basement of the Thieves Guild's mansion, Bobby is on the left, and Pierre is on the right. When the shot changes, they have swapped places. (00:12:43)
Continuity mistake: When Wolverine runs up to Gambit's mini-jet, he puts a considerable amount of distance between himself and Jean Grey, and nearly makes it all the way to the jet and Rogue before the shot changes. When the shot does change, he is suddenly several feet back from where he just was, and Jean Grey is now right behind him. (00:09:01)
Continuity mistake: When Gambit lands his mini-jet in the swamp, it's in an open area. When Wolverine, Rogue, and Jean Grey find his plane shortly after, it is now parked next to a tree and some foliage. (00:07:48 - 00:08:56)
Deliberate mistake: When Gambit and Pierre are boating down the river, in the shot of Pierre saying "Yeah, we got word," the trees they pass on either side of the screen are just the same tree drawn repeatedly. (00:08:08)
Continuity mistake: When Wolverine enters the infirmary, Cyclops is resting his right hand on his lower abdomen area with his fingers extended. When the shot changes, his hand is a closed fist and has moved closer to his chest. (00:07:37)
Continuity mistake: When Bella Donna is being selected as the chosen one for the Guild of Assassins, she is flanked by three of her guild members. When the shot changes, the three guild members have disappeared. (00:06:49)
Continuity mistake: When the chosen one for the Guild of Thieves drops his tithe box, it lands on the inside of his right foot. When the shot changes, the box is suddenly equidistant between his feet. A couple of shots later, the box has moved away from him, resting next to the tree stump. (00:06:17)
Continuity mistake: In the flashback when Gambit runs up to two of his fellow guild members to tell them the others are almost there, he runs up to the one in the blue vest. When the shot changes, he is suddenly facing his brother Bobby. (00:05:21)
Continuity mistake: When the Danger Room alarm is beeping to notify Rogue that Cyclops is in danger, in the first shot, the control panel for the alarm consists of the screen and rows of buttons below it. When the shot changes, about half the rows of buttons have been replaced by what appears to be a phone. (00:03:57)
Revealing mistake: When Gambit bumps the toggle switch that increases the Danger Room difficulty, you can see it actually moves itself before his elbow touches it. (00:02:55)
Continuity mistake: When Gambit answers the phone, he brings it to his right ear with his right hand. When the shot changes, he is holding it to his left ear with his left hand, and he is also facing the opposite direction. (00:02:53)
Continuity mistake: When Gambit is asking why Cyclops wants his Danger Room session to be tougher, there is a microphone a few inches from his mouth. When the shot changes, the microphone has disappeared. (00:02:44)
Continuity mistake: When the Danger Room monster has ensnared Cyclops, the slime coming off its tentacles is green. When the shot changes, the slime is orange. (00:02:18)
Continuity mistake: When Xavier and Magneto are trying to escape from Vertigo, Xavier cuts the ropes of the bridge they are on, leading him and Magneto to swing into the cliff wall and hop down safely to a ledge below. When they look back up at Vertigo, she is at roughly their 10 o'clock, with the other side of the bridge by her feet. Considering that they just dropped down onto the ledge and have only moved a couple steps to their left, the other side of the bridge should still be directly across from them. (00:15:45)
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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