Plot hole: When Sarah Paulsen pulls the necklace out of the water, the necklace clasp is obviously closed. Since the circumference of the necklace is too small to fit over the top of Anne Hathaway's head, why would anyone believe that it fell off her when she was running to the bathroom? The only way that could have happened is if the clasp (which we were earlier told can only be opened by a magnet) had opened. The trained security guards wouldn't have suspected something wasn't right about a closed necklace falling off over of her? They were following her. They saw that at no point did she lower her head on her way to the bathroom for the necklace to fall off over her head to begin with. It also could not have fallen off her when she was vomiting into the toilet in the bathroom since the clasp was closed. (01:18:25)
Plot hole: As shown when Robin comes under the influence of Slade's mind control device, the hypnotized people retain their abilities and higher intelligence, just with a loyalty to Slade. That being said, when Slade hypnotizes all the DC heroes, Superman and The Flash are among them in the theater. Slade orders all the heroes to chase after and destroy the Teen Titans. The Titans take off on foot with the others running after them and are able to keep their distance in a big chase sequence. Superman and The Flash never use their super speed to over take the Titans, which would have been so very easy.
Plot hole: During the climax with Van Helsing and the Kraken the writers of the film seemed to have forgotten about the powers Dracula has always had. At no point does his super speed or indestructibility ever come into play, he could have easily climbed up to the DJ booth and dealt with Van Helsing in seconds instead of going through the silly DJ battle.
Suggested correction: The kraken was faster and stronger than Dracula, if you watched he kept trying to reach the DJ booth and fight but was stopped each time and nearly crushed. It was said that the kraken was extremely strong and the only thing that could subdue him was a more powerful song than the other.
Plot hole: *SPOILER* Calvin's twin sister and mother were killed years earlier in an automobile accident. Calvin kept going to his doctor with "new symptoms", insisting there was something physically wrong. Dr. Collins told Calvin, "Your health issues aren't physical. I thought sending you to that support group would give you a better perspective." The doctor should have referred Calvin to a psychiatrist for a diagnosis and, if appropriate, the psychiatrist would recommend therapy or a support group. (00:10:15)
Plot hole: Kate could not get Leo's photo in order to get his passport.
Suggested correction: He was rich and famous, they had no problem finding information about him online, so could have found a suitable photo online (photoshopping it if needed).