Continuity mistake: On his own computer, Sean looks up his son's file, which states the boy died immediately and his date of death was September 9th, 1991. When Eve and Castor (as Sean Archer) are at the cemetery, the date of death on the headstone is September 24th, 1991. (00:21:15 - 01:14:50)
Continuity mistake: When Castor (as Sean Archer) is speared, as he stands there singing morosely his shirt is drenched in blood, but when he is next seen in the ambulance that blood on his shirt has vanished. Additionally, the cuts on his face produce blood trails which smear, when he is first speared, but in the ambulance his face is cleaned up and the blood trails are thin and neat.
Continuity mistake: When Archer and Dubov are making their escape, Dubov falls over the rail and Archer catches his gun barrel then tries to save him. In the last shot before Dubov falls, Archer is holding on to the very last tip of the gun, but in the wide shot he is holding a lot more of the barrel.
Continuity mistake: After the second speedboat explodes, when Sean (as Castor Troy) pulls the speargun trigger, Castor (as Sean Archer) grabs the spear shaft before it can unload. As he grips the gun, the problem is that in some shots the slings are still loaded, but in other shots they are not. (02:09:00)
Continuity mistake: After being told that Pollux was released from prison, Sean Archer (as Castor Troy) shouts that he's Sean Archer, then grabs hold of the bars above him, with three bars between his hands. Next shot, as the guard's foot is on his hand, there are only two bars between his hands before he lets go. (00:58:50)
Continuity mistake: During the speedboat chase, when Castor Troy (as Sean Archer) shoots up the white speedboat that Sean (as Castor Troy) drives, there are numerous bullet holes on its starboard side. Four shots later, when he hits the box on the rear seat, those bullet holes on the starboard side are gone. (02:04:15)
Continuity mistake: Eve and Troy visit Mikey's grave. When they first go out to the car, it's cloudy and raining, but they get to the cemetery and the sun is out and everything is completely dry.
Continuity mistake: After the jet crashes into the hangar, Sean Archer runs up the back end of a police cruiser, whose three blue flashing lights are completely shattered. In the next shot facing him, when he reaches the car's roof, two of the blue lights have repaired themselves. (00:13:45)