Revealing mistake: When they are on the border of Danube in Budapest, and the Bride is inviting them to a ball, look across the river at the large building with a golden dome. It's the National Theatre situated in Prague, Czech Republic, where the scene was shot.
Continuity mistake: When Anna is running away from the Wolf Man she is wearing felt shoes but when Velkan pushes her out of the way she is back wearing her high heeled boots.
Continuity mistake: Near the end of the attack of the Brides, Marishka is about to make her final "charge". The wind blows the hair back from her face, showing that she is not wearing any earrings. Yet after Van Helsing kills her and she starts to disintegrate, she is wearing large triangular dangling earrings. (It's not because her jewelry disappears in her flying form - she is shown wearing bracelets and rings in *both* forms).
Continuity mistake: In the scene in the village, after the brides have attacked, Anna lands on top of Van Helsing. In one shot she is sitting with her legs under his arms, in the next shot she sits above his arms. When they roll, her legs are back under his arms.
Factual error: In the scene where Anna is carried in the air with the city of Budapest appearing in the background, there are two columns in the top right corner which haven't been edited out even though they are chimneys of factories built in the 1950's.
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: During Dracula's ball, when Anna looks into the mirror after Dracula lowers her, the reflection shows an entirely empty room. Even though the vampires don't cast any reflections, the furniture should still be seen in the mirror.
Continuity mistake: In the scene where Van Helsing is fighting Dracula's brides for the first time, when the sun comes up and they disappear, there is a wooden table behind Anna when she stands up, and there's nothing on it. But a couple of shots later there is the dead body of a man on it.
Other mistake: When there is a werewolf transformation, the infected person's skin falls off to reveal the werewolf underneath. When changing back to human, the werewolf's skin falls off. When Van Helsing becomes a werewolf, his human skin falls off as he changes. As he battles Dracula as a werewolf, he grabs Dracula's throat. As soon as he does, the full moon is covered by the clouds and Van Helsing simply reverts to his human form. No werewolf skin falls off, he just changes back.
Continuity mistake: Anna wears high-heeled boots during the movie, but during some action scenes, they are flat-bottomed boots.
Continuity mistake: As revealed in the DVD commentary, the character Anna's hair changes somewhat in some scenes. Noticeable is the very slight changes that occur before she finds out her brother is a werewolf. An original mistake was already corrected, but I assure you it's there. It's just hard to see.
Other mistake: When Igor tortures the Werewolf behind the canvas, both of them can be seen as shadows, meaning a source of light is creating these images. When Igor hits the Werewolf with his staff, sparks can be seen through the canvas. First, as the image is a projection, the sparks would appear somewhere else on the canvas, and not exactly on the position of the staff's projected image. Even if the images are just silhouettes, the angle of the shot and the visible pillars indicate a much larger size then Igor really is. Second, such an intense source of light would alter the projection of the shadows a lot, not just a little bit in front of the Werewolf. In the case of silhouettes, they would completely disappear, as the source of light is between the 2 actors, and not at the side of them.
Audio problem: In the scene where the monster saves Anna by knocking down the last Bride, there is one shot where he turns to look at Anna framed in the window. His right leg support makes the hissing sound without any steam coming out of it.
Visible crew/equipment: When Dracula says "You can't kill me, Victor... I'm already dead!" in the beginning, pay attention. As the camera dramatically moves towards the two men, you can see the shadow of the camera appear on the lower half of Victor's face. It's not Dracula's shadow, because it appears after Dracula moves right in front of him, and perfectly coincides with the camera movement. There's also a brief flash of lightning, and the lightning shows that the shadow is very "boxy," unlike a human shadow.
Continuity mistake: After killing Dr. Frankenstein, Dracula has blood on his lips. After he uses his hand to wipe the blood away, no blood is on his hand.
Continuity mistake: When the movie begins and the villagers are raiding the castle, Dr. Frankenstein tries to sneak through a basement door. Dracula produces an explosion and Doc turns his head away. From the opposite angle it's still facing forward.
Answer: After being killed - "murdered" as Dracula stated several times - by Van Helsing, Dracula made a deal with the Devil to regain his life. Carl tells his story when telling Van Helsing and Anna everything that he has learnt.