Revealing mistake: When Beast is entering Carly's room to see if her procedure was a success, he passes through the door frame. (00:11:08)
Mojovision - S2-E11
Revealing mistake: When Sauron is first shown flying towards Shanna, the edge of an animation cel is briefly visible on the right side of the shot, going over a jungle fern. (00:19:54)
Revealing mistake: When Wolverine notices Slab running off with Jean Grey, you can see the edge the animation cel moving across the screen from left to right. (00:12:34)
Mojovision - S2-E11
Revealing mistake: When Jean is dodging the Punisher robot's gunfire, the edge of an animation cel is visible, most noticeable when she is starting to form a telekinetic bubble around herself. (00:16:38)
Time Fugitives: Part 1 - S2-E7
Revealing mistake: When the electronics store manager collapses onto the display stand, if you look closely, you can see the business cards he falls onto fly into the air before his head makes contact with the stand. (00:08:23)
'Til Death Do Us Part: Part 1 - S2-E1
Revealing mistake: After Morph laughs when the police have shot Storm out of the sky, there is a split-second flash of the establishing shot of the Veteran's Building Jubilee went to a little earlier in the episode. Note, this mistake may only occur on Disney+. (00:20:31)
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)
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)
'Til Death Do Us Part: Part 2 - S2-E2
Revealing mistake: In the second shot of Rogue and Beast standing outside the hospital, you can see they are floating about a foot above the sidewalk. (00:05:16)
'Til Death Do Us Part: Part 1 - S2-E1
Revealing mistake: When Morph has sabotaged Beast's Danger Room session, the same shot of Beast running away from the projectile apparatus is used twice. (00:18:08)
'Til Death Do Us Part: Part 1 - S2-E1
Revealing mistake: When Morph, disguised as Storm, is walking into the kitchen to talk to Jubilee, he appears out of thin air. (00:15:37)
Revealing mistake: When Morph is saying "You never were very bright," part of his shirt collar has been drawn on his chin. (00:07:20)
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)
Time Fugitives: Part 1 - S2-E7
Revealing mistake: When Wolverine is free falling from the Blackbird, his left leg passes through Cyclops' right arm. (00:11:40)
Mojovision - S2-E11
Revealing mistake: When the X-Men are being returned to the electronics store, there is a noticeable jump-cut (odd for a cartoon) just before Wolverine materializes. (00:18:40)
Mojovision - S2-E11
Revealing mistake: When the Gladiator robot shoots an optic blast at Wolverine, you can see the hole in the chest area of Wolverine's uniform is already there before the blast hits him. (00:16:24)
Mojovision - S2-E11
Revealing mistake: When Mojo's studio audience is cheering after he says "I give it two flippers up," you can tell by each character's celebratory movements that it is just a reverse of the shot where the audience was first shown earlier in the episode. (00:07:50 - 00:15:23)
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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