Corrected entry: In the big fight scene at the end of the movie against The Brotherhood, Storm fights Callisto (Speed/mutant-detector) and kills her via electricity which comes out of her hands. Since Storm's power is to control weather, and weather control and electric shock are two very different things, she shouldn't be able to do this (in the first movie she had to summon lightning down from the sky to use against Toad).
Corrected entry: In the scene where Juggernaut is attempting to catch Kitty Pride and Leech, he runs and ends up hitting his head on the wall and knocking himself unconscious (due to the fact that Leech has the ability to nullify other mutants' powers). However, Juggernaut is not actually a mutant, as his power is derived from the suit he wears (an alien suit). Therefore, in reality he would have still bashed through the wall and Leech's power would have had no effect on him at all.kordhendry
Corrected entry: In the scene where Jean and Magneto are overlooking the camp of mutants, Magneto talks to Jean about her powers. He holds up the weapon with the antidote and says he can only control metal then levitates the weapon. The weapon was supposed to be made of plastic as revealed later in the movie. The alternate scene shows him levitating a metal mug instead which made sense with his line.
Corrected entry: When Shadowkat meets Leech in the complex, she can't phase through the wall to escape because being near Leech negates her mutant powers. When Juggernaut enters the same room, he is unable to break through the wall for the same reason, however Juggernaut technically isn't a mutant, his abilities were received through mysticism so his powers shouldn't have been affected.
Corrected entry: In the scene where Rogue talks to Wolverine about going to get the cure, she reveals that her real name is Marie. In the first X-men film, Rogue introduces herself to Wolverine as Marie after he reveals that his real name is Logan therefore eliminating the need for her to reveal her name in the third film.
Corrected entry: Juggernaut's power is the ability to gain great strength but only by building momentum. This was proved when the loss of momentum, by locking his arms and legs down in the mobile prison, is how they were able to contain him. However, when Kitty Pryde sinks him in the floor, he bursts out effortlessly, despite having his arms and legs fully pinned down in concrete and unable to gain momentum.
Corrected entry: When we see Magneto move the Golden Gate Bridge to Alcatraz he sets it down so that there is a bridge across the mainland to Alcatraz. The bridge is supported only by the island and the mainland, this wouldn't happen as a bridge that long and heavy would just collapse in the middle, that is why suspension bridges with supports in the middle are needed.
Corrected entry: In the second film Magneto escapes the entire prison with only the aid of 3 ball bearings. He could have easily ripped the cars apart and used them as bullets against the troops guarding Lech and hit them with 100% accuracy or even made the cars spin like tops and slam into the guards. All he did was throw cars in random directions and let Pyro light them and hope for the best. This goes beyond a character mistake, as Magneto's often been shown to make very good use of metal around him, whereas here he just doesn't bother so it benefits the plot.Spaceboy_007
Corrected entry: When the troops start mobilising to attack the Brotherhood, they make a big show of removing 'all metal' from their gear. However, multiple times the soldiers are shown using radio equipment built into their helmets. Even if they replaced everything they could with plastic, electronic impulses still require metallic wire to operate, and since in X2 Magneto made good use of iron injected into someone's bloodstream, a decent collection of wires would definitely have been enough for him to use to kill the troops.
Corrected entry: In X-Men 2, we see a shot of Hank McCoy on a TV screen in a bar, who is not blue and covered with hair. In X3, they act like they've known him for years that way. He even mentions his old uniform not fitting him.
Corrected entry: When they first attack the bridge and everyone is escaping from their cars and jumping off the bridge, none of the cars have their lights on. Yet after darkness suddenly falls (see the other mistake), all the lights on the cars on the bridge are all on, despite no-one being left in their cars to have turned them on.