Continuity mistake: When the External states the Guild of Thieves have dishonored the tithe, both the Thieves' and Assassins' tithe boxes are missing from their respective tree stumps. (00:17:10)
Continuity mistake: When the External is emerging from the water, the Thieves Guild's tithe box is missing from its respective tree stump. In the next shot, it is back in place. (00:16:30)
Continuity mistake: When Rogue flies back towards Gambit and Bella Donna, Bella Donna is standing behind Gambit. When the shot changes, Bella Donna is standing in front of Gambit. (00:15:35)
Continuity mistake: When the Thieves and Assassins guilds begin to skirmish, they start by trying to regain the weapons that Jean Grey telekinetically confiscated from them. A couple seconds into the fight and most of the weapons have disappeared altogether. (00:15:20)
Continuity mistake: When Gambit pushes Bella Donna over, she is on his left, and there is a tree stump on his right (out of shot). When the shot changes, she is up against the tree stump. (00:14:25)
Continuity mistake: When Gambit is looking at himself in the mirror while wearing a tuxedo, you can see in his reflection that he is barehanded. In the next shot when he removes the tuxedo, he is wearing his usual black gloves. Also, the rose on the tuxedo goes from being on his right side (reflection's left) to being on his left side just before he removes the tuxedo. (00:13:15)
Continuity mistake: In the first establishing shot of the Assassins Guild's mansion, there is a stairway leading up to the front door. In the establishing shot of the mansion in the scene where Gambit is in Bella Donna's bedroom, the stairway is missing, and consequently the mansion's porch area isn't as high off the ground. (00:09:20 - 00:13:20)
Continuity mistake: The cell that Bobby was held captive in is noticeably smaller after he is set free. (00:09:55 - 00:11:40)
Continuity mistake: After Bobby is set free, Gambit, Bella Donna and her henchman remain in Bobby's cell. When Bella Donna begins torturing Gambit, the two of them are suddenly alone in the cell. (00:11:20)
Continuity mistake: When Bobby starts walking out of his cell, Gambit has his back to him. When the shot changes, Gambit is suddenly facing him. (00:11:15)
Continuity mistake: The two assassins standing guard outside the Assassins Guild's mansion have swapped sides when they let Gambit in the front door. (00:09:25)
Continuity mistake: After Jean Grey, Rogue and Wolverine locate Gambit's mini-jet, they land the Blackbird behind a row of plants. When they emerge from the Blackbird, the plants have disappeared. (00:08:55)
Continuity mistake: When the chosen one for the Thieves Guild tries to present their tithe to the External, he is shown walking right up to the tree stump where he was to have placed the tithe. When the shot changes, he is still walking forward, and therefore should've bumped into the stump. He is saying a line of dialogue as he is walking forward, so it can't be considered an action shown from a different angle. (00:06:15)
Continuity mistake: When the chosen one for the Thieves Guild is called forward to present their tithe, the chosen one for the Assassins Guild can still be seen kneeling before the External. In the next shot when the chosen one for the Thieves is shown arriving on the scene, the chosen one for the Assassins is suddenly back to standing among the other members of his guild. In the next shot, the chosen one for the Assassins is back to kneeling before the External. (00:06:00)
Continuity mistake: During Gambit's flashback, the chosen one for the Assassin's Guild is shown to be placing their tithe box on the stump of a tree roughly halfway between the center ring and the outer edge. When the shot changes, the tithe box has suddenly moved to the center of the stump, and the tithe box itself is suddenly wider and shorter and has rotated 90°. (00:05:00)
Continuity mistake: The position of Cyclops' body changes when Jean Grey is cradling his head. At first, he is sitting slightly upright. When the shot changes, he is lying down. (00:04:40)
Continuity mistake: The amount of damage to Cyclops' uniform decreases. When his Danger Room session is first terminated, his uniform is mostly missing around his shoulders and chest. A few shots later, the aforementioned area of his uniform is not as torn up. (00:04:15 - 00:04:50)
Continuity mistake: The size of the hole beneath the trap door in the Thieves Guild's mansion changes. When Wolverine, Rogue and Jean Grey are shown falling down it, it is easily large enough for the three of them to fall down without bumping into each other. When we see the hole in the ceiling after Rogue destroys the wall that was falling on her, the hole is barely large enough for one person to fit through. The hole also moves closer to the back corner of the room, whereas it appeared to be closer to the back-center of the room once they landed.
Continuity mistake: The orientation of Gambit's mini-jet respective to the Blackbird changes. When the Blackbird first lands, the mini-jet is perpendicular to it. When Wolverine, Rogue and Jean Grey go over to inspect the mini-jet, it is suddenly parallel to the Blackbird.
Continuity mistake: Shortly after Wolverine, Rogue and Jean Grey enter the Thieves Guild's mansion, they fall down a trap door. However, the trap door is not there when they first enter the mansion, instead only appearing in the shot where they step on it.
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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