Revealing mistake: When firing the crossbow, Van Helsing runs out of arrows, but the bow's canister is completely full of arrows. In the same shot the canister spins once and they all disappear. (00:25:55)
Revealing mistake: When Dracula is walking upside down, and he yells "Let us Begin.", you can see the wire and pulley device supporting him underneath his feet, in between the sides of a pre-cut line on the top side of the bridge. (00:51:10)
Revealing mistake: When Van Helsing enters the secret-society under Vatican City, in the distance you can see a giant mirror used to reflect the set to create the illusion that the room is much bigger than it really is. You can see Van Helsing and the priest's reflections at the top corner of the screen several times (Confirmed on DVD commentary). (00:14:45)
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 a bit easier to see in slow-motion. (Though slow motion is not required). (01:52:15)
Revealing mistake: When Dracula walks up the wall (the first time we see him in color), in the overhead shot the torches wobble slightly from where the separate photography was composited in. (00:34:25)
Revealing mistake: At the ball when Carl pushes the man spitting fire so that he spits fire on Dracula, you can see Dracula grabbing him and throwing him away. Then it cuts to Van Helsing gliding down on a rope grabbing Anna. When we get to the scene where the camera view comes flying against Anna we can see, on the left, Dracula's shadow when he is throwing the man. As the previous scene where Dracula threw away the man was most likely done with CGI, they forgot to add the man's shadow in this scene. Also in the following scene you can see Dracula throwing, but this time they forgot to add the man in. (01:23:35)
Revealing mistake: When Velkan and the werewolf has dived off the cliff, we get a shot behind Anna where she is looking down the cliff. It cuts to a front shot of her and back behind her again and you can see it's actually the same scene played over again. You can easily see it on how her hair moves in the wind. (00:22:00)
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. (00:59:35)
Revealing mistake: At the windmill when the fire reaches the cases with Absinthe bottles the cases explode. Howeverm when the explosion occurs we can see sparks. I'm pretty sure an explosion like this wouldn't produce sparks, so it's obvious the explosion was ignited by some explosives. (00:05:35)
Revealing mistake: When the undertaker is about to hit Van Helsing with the shovel, we can see the shovel stop in the air before Van Helsing grabs it. (00:44:50)
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.
Revealing mistake: When the windmill starts to burn, we see a closeup of the Bible, before fire flares up in front of it. But if you look close, the angle of the fire is not correct in relation to the angle of the camera. Obviously the foreground fire was imposed over the scene later on. (00:05:35)
Revealing mistake: When it shows one of Dracula's brides drinking a glass of blood, close-up shots reveal it's actually tomato juice, shown by traces on the glass itself. (00:30:35)
Revealing mistake: When Dr. Frankenstein is holding the sword against Dracula, you can see its shadow on the wall to his left. However, when Dracula impales himself with the sword you can see the sword's shadow going through Dracula's shadow at the same time. Whatever the film makers have done, they have forgotten to remove the sword's shadow. (00:03:30)
Revealing mistake: When Verona grabs Van Helsing of off the chariot/coach, you can see the special effect of her claw holding Van Helsing is not quite matched up. The claw "wobbles" slightly over Van Helsing's arm. And this does NOT have to do with the fact he is struggling. (01:12:50)
Revealing mistake: In the beginning when the Frankenstein Monster throws the equipment on Dracula you can see the outline where the wire used to drag Dracula backwards is attached. (00:04:10)
Revealing mistake: When Carl throws the new canister of arrows to Van Helsing during the vampire attack on the town, you can tell that when the camera cuts, Hugh Jackman just tossed the canister up in the air and grabbed it as it fell. The motion and angle at which is falls doesn't match up to the shot where Carl throws it. (00:26:00)
Revealing mistake: When the baby vampire lands on the bride's hand and then flies off her arm movements seem funny as if there was actually nothing there and she had to pretend something landed and then flew off. (00:54:50)
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.