Night of the Sentinels: Part 1 - S1-E1
Plot hole: Wolverine bails out on the mission to destroy the files at the Mutant Registration Center to instead go look for Jubilee after she goes missing. When the rest of the team arrives, Wolverine is already there waiting for them. They flew to the Mutant Registration Center in a jet and their mission briefing heavily implied that they needed to leave immediately, so there is no way Wolverine could have arrived before them if he was off looking for Jubilee first.
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.
Sentinel never sank into sand in other episodes.
Well, it's shown here.
Slave Island - S1-E7
Plot hole: When the Leader says "Take me to my car at once!", one of his guards goes to open the door to the room only to have Cable shoot the door with his plasma rifle. The Leader then says "The other way you fool!" and everyone in the room starts running for the windows that Cable shot out a few minutes earlier, which happened to be the only other way out of the room. As evidenced earlier from when Cable shot the windows out, that particular floor appears to be 8 stories up, so if everyone in the room exited through the windows, they would have all fallen to their deaths as all of them were regular humans with no superpowers. (00:17:40)
The Unstoppable Juggernaut - S1-E8
Plot hole: After Wolverine deduces that Colossus wasn't the person who destroyed the X-mansion and Colossus walks away, Jubilee gets a phone call from Rogue literally less than 30 seconds later informing them that the bank was being robbed by somebody big who is later revealed to be the Juggernaut. Wolverine (now wearing a different set of clothes) and Jubilee are then shown arriving at the bank in Wolverine's jeep just in time to see Colossus being arrested for the crime while claiming he was only trying to open an account and stop the robber. If the robbery was being committed while Colossus was fighting Wolverine, then the police and bank employees would have known Colossus was not the perpetrator, not to mention the bank would have been closed off to the public, effectively preventing Colossus from going in to open an account in the first place. The only way Colossus could have feasibly been implicated would be if he was at the bank the same time that Rogue called Jubilee, which he obviously could not have reached the bank in that amount of time since Wolverine had to drive there.
Plot hole: After Wolverine tells Gambit that he only knows how to pick pockets and steal candy from babies, Gambit attempts to retaliate by kinetically charging one of the bricks Wolverine is working with in order for it to blow up in his face. Anything Gambit kinetically charges makes a high-pitched humming sound, and Wolverine possesses a superhuman sense of hearing, so he should not have been caught unaware by it. (00:06:55)
Plot hole: Towards the end of this episode, Jean Grey nearly falls to her death when a concussion blast from Cable's gun knocks her off a cliff, only for her to be saved at the last moment by Rogue. Apparently Jean Grey and the writers for the episode forgot that her telekinetic powers give her limited flight ability as well as the ability to slow falls, both of which she has demonstrated in other episodes.
Days of Future Past: Part 2 - S1-E12
Plot hole: When Gambit charges an object with kinetic energy, it makes a high-pitched sound. When he places a charged card on the arcade game to use as a trap, Wolverine should have heard it, as he possesses a superhuman sense of hearing, especially since Gambit muted the TV. (00:09:28)
Plot hole: Magneto states that he went to Washington, DC to witness Senator Kelly's assassination. But Magneto had no way of knowing about the assassination plot. Mystique was the one who was attempting to assassinate Kelly, and Apocalypse was the one who carried out the order. At this point in the show, Magneto had not worked with either Mystique or Apocalypse, and it's highly doubtful that Mystique would leak the plot, since it was supposed to be covert.
'Til Death Do Us Part: Part 1 - S2-E1
Plot hole: The establishing shot of the White House indicates that President Kelly's press conference is taking place there. A member of the Friends of Humanity disguised as a mutant busts into the room and starts terrorizing the reporters and destroying everything. The Secret Service would have either detained or shot this man long before he could have even gotten close to the press conference. Graydon Creed also shoves a security guard that tries to intervene but somehow isn't arrested for it. (00:05:50 - 00:06:35)
Plot hole: After Magneto and Xavier discover that their powers have vanished, Mr. Sinister is shown to be watching them through surveillance footage, zeroed in on their faces from a straight angle. At this point, Magneto and Xavier are standing at the edge of a cliff in the Savage Land, which is a jungle hidden in Antarctica. There's no conceivable way Mr. Sinister could have security footage of them from where they are located. Any camera would have to be mounted onto a tree, and the cliff is at a considerably higher elevation than the jungle itself, as well as a considerable distance away. Even if Mr. Sinister was able to zoom in on them from such a distance, the treeline being lower than the cliff would only allow him to view them from a low angle, and that's only if the cliff wall didn't obscure them. (00:20:00)
Plot hole: In the season one episode The Cure, when Pyro and Avalanche are in the bar on Muir Island waiting for Mystique to arrive, Avalanche says "This friend of yours better show up soon or I'm going back to jail, just for something to do!" Rogue then comes in and Pyro suggests to Avalanche that Rogue could be Mystique, to which Avalanche responds "What do you mean it could be? Don't you know what she looks like?", leading Pyro to tell Avalanche that Mystique is a shape-shifter. This dialogue implies that Avalanche has no idea who Mystique is, which is further substantiated when Pyro and Avalanche kidnap Mystique later in the episode while she is in the guise of Dr. Adler, and Avalanche didn't recognize Mystique when she revealed her true form. However in this episode it is shown that Pyro and Avalanche were both previously members of Mystique's Brotherhood of Mutants, so Avalanche should already know who Mystique is without Pyro having to tell him. Rogue was also a member of that group yet neither Pyro nor Avalanche recognize her.
Plot hole: After Beast and Dr. Bohlson leave Carly's room, they briefly chat in the hallway just outside the door for less than 15 seconds in real time, and then discover that in that brief time frame, the Friends of Humanity abducted Carly from her second-story room via the window, managed to incapacitate the nurse, security guard and Carly's father, toss around furniture and spray paint "For Humanity" on one of the walls, all without any of the victims making a sound or the Friends of Humanity making a sound themselves. The Friends of Humanity aren't ninjas, rather they are shown to be somewhat bumbling, so there's no way they could have done all that as quickly and quietly as shown. (00:12:30)
Mojovision - S2-E11
Plot hole: Spiral comes into the Earth dimension through the multiple television screens, teleports all X-Men members present to Mojoworld, and then retreats back into Mojoworld herself the same way she left. When the action shifts to Mojoworld, Rogue is among the captive X-Men despite the fact that she was not among the ones Spiral abducted. (00:07:10 - 00:08:05)
The Phoenix Saga (2): The Dark Shroud - S3-E4
Plot hole: After Professor X crashes his mini-jet onto the hospital roof and loses consciousness, he isn't discovered until Jean mentally locates him. An aircraft crashing on the roof would cause enough noise to immediately alert staff and anyone else in the hospital of his predicament. (00:09:15 - 00:15:45)
The Phoenix Saga (2): The Dark Shroud - S3-E4
Plot hole: Wolverine's enhanced sense of smell should have alerted him to Erik the Red's spy on the roof. Failing that, the video feed Erik the Red is receiving from the spy shows Wolverine, Beast and Professor X looking right in the spy's direction, so they would have seen him. (00:15:55)
The Phoenix Saga (4): The Starjammers - S3-E6
Plot hole: Corsair takes out the X-Men by having Raza calibrating their stun weapon to humans. Since Corsair is also a human, the blast renders him unconscious along with the X-Men, and the Starjammers take him away. When Wolverine and Phoenix regain consciousness, they realize that Cyclops has been taken by the Starjammers as well. The problem is since Corsair was unconscious, he couldn't have possibly ordered the Starjammers to take Cyclops with them, and the Starjammers had no reason to take Cyclops of their own volition. Raza even acknowledges that Corsair is the one that takes Cyclops. (00:08:15 - 00:09:00)
The Phoenix Saga (4): The Starjammers - S3-E6
Plot hole: Rogue is able to punch Gladiator and knock him off his feet, yet in the previous episode when the Juggernaut punched Gladiator he didn't even budge. The Juggernaut is a lot stronger than Rogue, so either Juggernaut's punch should have affected Gladiator or Rogue's punch should not have. (00:17:55)
Savage Land, Strange Heart (1) - S3-E8
Plot hole: When Kazar discovers that Sauron is really his friend Karl Lykos, Lykos reveals that he was turned into Sauron by Mr. Sinister. However, in the season 2 episode Mojovision when Sauron was attacking Shana, Magneto already knew who Sauron was. Magneto was the master of the Savage Land mutates years before Mr. Sinister was and hadn't been to the Savage Land for many years before then, so if Magneto already knew who Sauron was, then it couldn't have been Mr. Sinister who created him. (00:19:46)
The Dark Phoenix (3): The Dark Phoenix - S3-E13
Plot hole: When the X-Men are on the roof of the Hellfire Club confronting the Dark Phoenix, Beast suddenly has some kind of hi-tech backpack-like device, despite being held captive without it in the previous episode, and never shown having one when he entered the club in the episode that preceded that one. (00:03:00)
The Dark Phoenix (4): The Fate of the Phoenix - S3-E14
Plot hole: Jean Grey decides to wear her original X-Men uniform in her trial-by-combat. But how could she possibly have had the uniform with her? She wasn't wearing it when the X-Men were suddenly and unexpectedly abducted by the Shi'ar and taken into outer space, and the Shi'ar weren't about to let Jean go back home and grab it. (00:07:10)