Slave Island - S1-E7
Plot hole: After Storm's attempt to escape the Genoshan prison is thwarted, she ends up in the ocean right at the shoreline of the beach, where she is captured by a Sentinel. Aside from the fact that it makes no sense for a Sentinel to be hiding in the ocean in the event that a mutant tries to escape the prison, there is absolutely no way that a two-story tall robot could hide in the ocean right by the beach, as the water would be way too shallow. You can even see that the water level only goes up to the Sentinel's ankle area when it is standing upright in the ocean. (00:03:15)
Suggested correction: Perception. (1) The Sentinel isn't as close as it appears. If it were close, then she would have been caught in its waves as it emerges. Also, she would be looking only at its chest circle. It's several yards away. (2) She washes ashore. She fell from the sky. She couldn't have fallen from that great height into shallow water without hitting bottom. (3) It's also a two-story tall robot. Its weight would sink it into the sand. So it could have very well been down that deep.
The Juggernaut Returns - S3-E17
Trivia: When the new Juggernaut crashes through the film studio, the production being filmed is a parody of Mighty Morphin' Power Rangers. There is even a short musical phrase similar to MMPR's theme song. (00:16:10)
The Dark Phoenix (2): The Inner Circle - S3-E12
Continuity mistake: Rogue rips off Donald Pierce's cybernetic left arm, but when he is first shown running away, his right arm is the one that is missing. When he catches up with Sebastian Shaw in the secret passageway, his left arm is back to being the one missing. (00:18:30)
Days of Future Past: Part 2 - S1-E12
Factual error: When Gambit is inside his mini-jet after escaping from Bishop and Wolverine, his radar screen says "Washington D.C." but the graphic above it is Washington state.
Continuity mistake: Wolverine first enters the sewers by ripping away a fence in the subway. When Jubilee and Gambit follow him, the fence is still intact. When they get closer it is torn again. Odd, really, because on the whole this show has few continuity errors, like self-mending clothes in other cartoons.
Time Fugitives: Part 1 - S2-E7
Factual error: Costumed superheroes notwithstanding, Bishop wouldn't be allowed to bring his gun into the United States Capitol. (00:14:40 - 00:16:10)
Days of Future Past: Part 2 - S1-E12
Revealing mistake: When Gambit draws a card from his sleeve to use as a trap, the gloved part of his hand that is below the pocket is translucent. (00:09:28)
Continuity mistake: When Storm is watching TV with her arms folded, her left hand shows her index and middle fingers touching. When the shot changes, it is her middle and ring fingers that are touching. (00:08:40)
Continuity mistake: When Archangel is lamenting his actions, the communicator devices from Storm's uniform are missing. (00:20:15)
Continuity mistake: When the three horsemen are climbing onto their mechanical horses, Famine's horse is in the middle, and Pestilence's horse is on the right. Once all three have all been individually shown to be mounting their horses, Famine and Pestilence have swapped places. (00:06:08)
Continuity mistake: When Gambit is saying "Someone may be tracking us," the snaps on both shoulders of his jacket are colored blue, when they should be the same brown color as the rest of his jacket. (00:11:45)
Trivia: One of the images in Gambit's mind-scan is of fellow Marvel Comics superhero Ghost Rider. (00:07:45)
One Man's Worth: Part 1 - S4-E1
Character mistake: When the civilians are fleeing the coffee shop, there are two spelling errors on the coffee shop's marquee. Firstly, the name of the coffee shop is Rip Van Winkle, but on the marquee, Winkle is spelled as "Winkile." To the right of that, Coffee House is spelled as "Coffe House." (00:16:55)
One Man's Worth: Part 1 - S4-E1
Trivia: The man that aids Wolverine in the coffee shop is Johnny Strabler, Marlon Brando's character from the film "The Wild One." (00:16:45)
Have Yourself a Morlock Little Christmas - S4-E12
Other mistake: When Gambit is tasting the food in the crock pot, his left arm has been drawn backwards.
Continuity mistake: When Gambit first walks into Bobby's cell, Bobby is sitting in a chair up against the back wall. A few shots later, Bobby is sitting in the center of the cell. (00:09:55)
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)
Family Ties - S4-E17
Revealing mistake: When Quicksilver is fidgeting inside his containment shell, the animators neglected to properly sync his body movement. You can see that his shoulders are not "connected" to his arms, as if his head and shoulders were separated from the rest of his body. (00:16:00)