Other mistake: Rogue's CGI model in the outro is missing the white streak in her hair.
Night of the Sentinels: Part 1 - S1-E1
Other mistake: In the scene where Professor X uses his psychic powers to deduce that Jubilee is trying to escape the mansion, there is a semi-dissolve edit that simultaneously shows a close-up of Professor X with his left hand on his forehead and a counterpart image of Jubilee hiding around the corner. If you look closely at Professor X in the counterpart image of Jubilee, his left arm and hand are shown to be on his hover-chair's armrest and not his forehead.
Night of the Sentinels: Part 2 - S1-E2
Other mistake: When the Sentinel throws Wolverine over the trees, you can hear him crash to the ground as soon as his body disappears from view. The ground in the area is flat with no tall hills, so Wolverine would require another second or two after clearing the treeline to crash to the ground. (00:10:24)
Night of the Sentinels: Part 2 - S1-E2
Other mistake: After Storm and Cyclops fly away from the barrage of Sentinels, one Sentinel is shown to have his right foot "floating" on top of the left foot of another Sentinel, almost as if their feet were occupying the same space. (00:11:25)
Other mistake: When the helicopters are attacking Magneto, they are firing their guns at him, and then he destroys them, at which point you can see the occupants parachuting away at the same time the helicopters explode. There's no way they could have been operating the guns and then jumping out of the helicopter to safety in one second. (00:06:01)
Other mistake: When Cyclops is turning on his communication device to talk to Storm, his fingernails have been drawn on his gloved hands. (00:18:50)
Other mistake: Whenever Rogue touches someone's bare skin with her own, it is accompanied by an energy surge to indicate she has drained them of their powers. However, when she is performing mouth-to-mouth resuscitation on Cyclops, the energy surge doesn't occur. (00:10:26)
Other mistake: When Xavier is in the War Room with the rest of the team showing where the closest he could pinpoint Cyclops and Jean's location is, he is sitting in one of the chairs positioned around the table. Xavier is paraplegic and usually sits in his own hover chair. While there's no reason he couldn't be sitting in a regular chair, it would be very impractical for him to do so, especially if he's just instructing his team where they need to go. (00:11:07)
Other mistake: When Gambit, Storm, and Jubilee get into the back of the taxi, you can see the window seat behind the driver is unoccupied, which would suggest the three of them are occupying only two of the backseats. (00:12:51)
Other mistake: When the hotel clerk is checking Gambit, Storm and Jubilee into their room, he determines that they are mutants by seeing footage of Storm using her powers at the Salem Center Mall from the very first episode. While it's not unreasonable that security footage from the mall could exist showing Storm use her powers, the footage also shows an extremely close zoom-in on Storm's left eye, which is extremely unlikely, unless the security camera somehow guessed she was about to activate her mutant powers. (00:13:27)
Other mistake: When Wolverine is walking around the camp after Sabretooth attacked it, he doesn't leave any footprints in the snow, even though Sabretooth's footprints are there. (00:14:52 - 00:15:36)
Slave Island - S1-E7
Other mistake: When Cyclops, Rogue and Jean Grey exit the War Room to depart for Genosha, at the top of the door frame there is a black spec moving around, possibly indicating that there was some debris or a clump of dust on the animation cells or the camera lens itself during filming. (00:08:15)
Slave Island - S1-E7
Other mistake: After Cable shoots his exploding plasma blast at the table that Gyrich, Trask, Hodge and the Leader are sitting at, the former three all evacuate the area while the Leader is still shown to be sitting at the table only a moment before it explodes, but he does not suffer any ill effects from the concussive blast or wooden shrapnel. (00:14:45)
Slave Island - S1-E7
Other mistake: When the Leader is backing away from Cable, his right hand and right foot pass through a puddle of water, but the water does not react to the movements. (00:19:05)
Slave Island - S1-E7
Other mistake: When Storm sends the Genoshan prison guard flying into the Blob, he knocks the Blob over. The Blob's powers prevent him from being moved, hence why he is sometimes called the Immovable Blob. Other episodes demonstrated his ability to stand his ground against force, such as being punched by Rogue or being blasted by Cyclops' optical beam.
The Unstoppable Juggernaut - S1-E8
Other mistake: When Wolverine is searching for clues as to who destroyed the mansion, he clears out some rubble to reveal two of Juggernaut's footprints. Given that the Juggernaut tore down the entire mansion, his footprints should be everywhere, not just in one spot. (00:04:10)
Other mistake: When Rogue is hovering above Muir Island, she pulls out a book to confirm she's in the right place, and the picture of Muir Island in her book shows it to have three smaller islands on its south side. When she lowers the book to look at the actual island, only the large island shown on the southwest side in the book is there. She's only hovering a few hundred feet above the island, so even though the other two islands were small, they should still be visible. (00:09:48)
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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