Audio problem: When the decapitated Sentinel body crashes to the ground, the sound of it crashing against the concrete is too soft for its size. It sounds like something slamming against a metal appliance when it should sound more like a car crashing into a wall, only louder.
Continuity mistake: After Gambit unlocks his collar, he lets the collar fall to the ground. In the next shot, the collar is visible on the ground a couple feet in front of him. In the shot after that when he retrieves the gun, the collar is no longer visible on the ground.
Continuity mistake: Before the mutants ambush the guards, they are walking in a single-file line, with Sunfire in front, followed by Jubilee, Mystique, Caliban, an unnamed female mutant, and Aurora. A couple of shots later, either Aurora or her similarly-dressed twin brother Northstar is suddenly at the front of the line.
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.
Continuity mistake: Gambit and Jubilee are shown to be grouping together what appears to be several pieces of malleable rebar. When the shot changes to Gambit reassuring Jubilee that Storm is alive, he is shown to be working with a single piece of rebar. When the shot changes again, they are back to working with a bunch of rebar.
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.
Add timeSerious B
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.
Add timeSerious B
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.
Add timeSerious B
Continuity mistake: When Cyclops is running through the mine to search for Wolverine and Gambit, he uses his visor to track their location. When the shot changes to a first person view through Cyclops' visor, the background is merely moving up and down. If he was running as the previous shot had shown, the objects in the background from his point of view would become larger as he got closer to them.
Continuity mistake: Jubilee destroys a Sentinel by tricking it into colliding with a train car full of tar and then using her powers to blast the car and cause tar to spill all over the Sentinel. After Jubilee is rescued by Rogue from the Sentinel that grabbed her from behind, the Sentinel that Jubilee destroyed, as well as the train car, have disappeared.