Revealing mistake: Xander has a XXX tattoo on the back of his neck. There are several scenes where you get a clear shot of the back of the stunt double's neck and there's no tattoo at all. Most noticeably in the scenes during the attack on the cocaine farm.
Revealing mistake: After X has put the bandaid explosives onto the motorbikes out the front of the compound, and is making an escape, he removes the bandaid off his bike and does a large jump over the castle wall. One of the bad guys is chasing him on another bike, and jumps the wall like X. As he is "flying" through the air, his long black trench coat remains hanging straight down. It should be flailing out behind him from his motion and the wind.
Revealing mistake: A rocket launcher that XXX shoots is clearly a camcorder with bits added onto it. You can see the viewfinder from a side shot, and the lens from the front.
Revealing mistake: When the AHAB launched its missile in the underground lab, it shows a shot of one of the scientists laying on the ground dead. You can see him breathing.
Revealing mistake: At the end of the movie, Czech Air Force sends two Sukhoi 22's to destroy Ahab, armed with rocket pods. When shown from the front, you can see the rocket pods are empty.