Continuity mistake: When Gambit is saying "You got me in the guild, Bobby," you can see on the wall across the hall that there is a switch that is the same red color as the wall. A few shots later, the switch is now gray. (00:10:18)
Continuity mistake: Bella Donna's engagement/wedding ring from Gambit doesn't appear on her finger until she mentions that she still wears it. (00:10:55)
Other mistake: When Bella Donna's henchman is letting Bobby go, he is shown to be walking over to Bobby empty-handed. After he unties Bobby, the tithe box has magically appeared in his hands. (00:11:10)
Revealing mistake: When the assassin is handing Bobby the tithe box, the assassin's left hand passes through the chair Bobby was sitting in. (00:11:15)
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: 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 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 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: Gambit's sleeves turn from black to pink when Bella Donna reveals to him that she double crossed the Thieves Guild. (00:13:25)
Other mistake: When Wolverine is threatening Pierre, there is a continuous shot lasting roughly 8 seconds in which Bobby is telling Rogue about Bella Donna, all the while Wolverine and Pierre remain in the foreground, and neither of them so much as moves a muscle in that 8-second span. Rogue also remains motionless for a majority of the shot. (00:13:35)
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 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)
Other mistake: When Gambit pushes Bella Donna down, the wedding veil that she was wearing comes to a stop in midair. (00:14:25)
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 Pierre is telling the Assassins that they betrayed the Thieves, he raises his left arm and points his finger at them, and then lowers his arm back down. When the shot changes, his left arm is raised again. (00:15:00)
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 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 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 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 Gambit places Bella Donna's ring on the ground, she is nowhere around it. When the shot changes, the ring is suddenly right next to her. Note: this mistake may only apply to the DVD version of the episode, as the version of the episode on Disney+ does have Bella Donna there when Gambit sets the ring down. (00:18:50)
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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