Other mistake: Van Helsing's ring fits his as a human, but in the climactic fight he turns to werewolf form and back and is still wearing it. He didn't have time to take it off and put it back on, so either one of his wolf fingers should be horribly, painfully cramped or the ring should have broken. No one insinuates that the ring has magical powers of any kind to prevent this.
Other mistake: The movie starts with scenes from a battle between Romans and Sarmatians. For a few seconds, we see a (very dark) shot of a warrior holding a severed head in his hand. That very same shot is used later in the battle between the Woads and the Sarmatian knights protecting the Bishop. Director's cut only. (00:01:05 - 00:08:30)
Other mistake: In the Arena Challenge scene, Nokama yells at Vakama to shoot the statue. In this shot, the back of her head passes through her armor, which cannot be possible with the actual Nokama figure. (00:21:49)
Other mistake: In the battle at Gaugamela scene where Cleitus jumps off his horse to help Alexander in the battle, Cleitus is seen cutting the head off a barbarian and throwing it at another. Two seconds later he is seen swinging that same head back and forth.
Other mistake: The Mustangs in the pen at the end are "wild" Mustangs taken from the Indians. When they are released from the pen, the camera shows them running. The sun shined on some of their hooves and they are shod (wearing horse shoes). Indians don't shoe their horses. They would not have shoes if they were truly wild or if taken from the Indians and there were too many in the pen to assume that the soldiers would have shooed them.
Other mistake: When Rebecca uses her computer to record movements in the greenhouse, the footage on its screen does not match with reality. (00:44:27)