Continuity mistake: When the girl gives Litwak her phone to show him there is a replacement part on eBay, her phones shows that it is connected to WiFi. Litwak doesn't set up his router until later that evening, he has only plugged it in. (00:09:41)
Suggested correction: It's possible she's either connected to wifi at another nearby business, using a public wifi signal, or using a friend's phone as a hotspot.
Other mistake: When Elastigirl is chasing the high-speed train, as she is in the middle of making her second final jump to reach the train, if one were to look closely, the train actually drives right past her before she lands. (00:31:40)
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.
Continuity mistake: The blue paint blob on the painting changes between shots. (00:47:00)
Continuity mistake: During the fight at Aunt May's house, May knocks Tombstone out of the house with a bat. The subsequent shots have him back in the house.
Continuity mistake: At the bank robbery when the girl and guy cop arrive, one of the thugs blasts the ground by the car causing it to flip and the guy falls out. But the girl stays in. However in the shot of it flipping you can see the both the front seats are completely empty with the girl not in the car. A couple of shots later when the guy is trying to help her out of the upside down car, she's in the passenger seat with the seat belt on. (00:02:20)
Continuity mistake: When the Nightmare Nurse is talking with Renee and looking out the window at the dark creatures that she can see, Renee responds and looks at her in the reflection of the window. When it cuts to a different angle showing her, the position of her head does not match her reflection. (00:17:40)
Continuity mistake: When Jason lunges at Batman with his knife, there is a pile of garbage by the wall where he lands. In the first shot the barrel by the garbage is wooden. But in the next shot it's suddenly a metal barrel/drum. It then changes back to a wooden barrel again. (00:04:20)
Continuity mistake: Princess Dawn is in her chambers and her servants are preparing her for the coronation. When her book-headed valet tells her "You have come of age", he is suddenly holding the tome with both hands, while he had just one on it before the cut. (00:19:30)