Continuity mistake: In the final fighting scene between Dracula and Van Helsing it can be seen that Dracula has all his fingers. However, later in the scene, when he asks Van Helsing for the return of his ring, one of his fingers is missing.
Continuity mistake: Towards the end of the movie, in the scene where Anna is taking the werewolf cure to Van Helsing and the vampire bride stops her on the large fallen pillar, she falls so she is in a sitting position with the cure in her left hand. She then switches it to her right. Then in the close-up shot, the cure is still in her left hand and she switches it again.
Continuity mistake: When Velkan hangs on the rope and is being pulled up he looks down and the werewolf climbs up the wooden pole and you can see scratch marks on the top of the pole. Then the second time he looks down at the werewolf you can see the top of the pole is scratch free and the werewolf makes the scratch marks again. If you have a close look at these two scenes you can see it's the same scene played twice, but with a different roaring sound from the werewolf.
Revealing mistake: When firing the cross-bow, Van Helsing runs out of arrows, but the bow's cannister is completely full of arrows. In the same shot he simply spins once and they all disappear.
Continuity mistake: When Anna and Van Helsing embrace to kiss, the hands with which they caress each other change position and even totally swap in between cuts. In one shot Van Helsing will be touching her with his right hand, the next shot with his left hand, the next shot with no hand, etc.
Revealing mistake: When Dracula pulls the silver stake from his heart, you can see it is a prop from the way the point wobbles slightly.
Revealing mistake: When Dracula is walking upside down, and he yells "Let us Begin.", you can see the wire and pulley device underneath his feet, in between the sides of a pre-cut line on the top side of the bridge.
Factual error: When Van Helsing goes to Rome, the subtitle refers to the Vatican as "Vatican City". By the 1880's the Pope had lost all his temporal power, and his previous lands (The Papal States) were taken by the new Italy. The Vatican had no lands or authority over any of Italy or Rome. The Pope was a virtual prisoner inside the Vatican. Only with the Lateran treaty in 1929 (with Mussolini) did the Vatican gain independence as the "State of Vatican City".
Continuity mistake: When Anna is hanging from the top of the roof, she places her feet against the wall before jumping. At that time you can see the wall is perfect without any cracks or marks. When it cuts to her leaping off you can see a huge crack going along the wall where she has her right foot.
Continuity mistake: When Dracula and Van Helsing meet for the first time, Dracula's hand placement changes between shots. This happens twice, once when he is saying 'But like me, hunted by all others." During this, his hands move from his side to taking his gloves off. And again, when he says 'You are the great Van Helsing,' his hands move from his sides to being in the air.
Revealing mistake: At the end of the movie, when Dracula's children explode, the goop from their bodies doesn't match up with the splashes on the ground. You can see some of it hit the ground and disappear, and other places, it would hit, then the splash would occur a second or two later. It was all computer-generated, so it was just slightly mismatched. Hard to catch normally, but easy to see in slow-motion.
Continuity mistake: When Velkan changes into a werewolf in front of his sister he still has tattered remains of pants on him. When he goes to Castle Frankenstein, and enters through the roof his pants are gone. When the Velkan werewolf lands on the ground and starts to change back, his pants are back on.