When Dave is drawing King Kong on the bus window, in one scene his arm is up, when he looks back at Becky it is down but when the camera is on him again it is still in a raised position.
In Chinatown after Dave has run away, Balthazar is turning his head and looking around the room. The man-doll in the left is without acupuncture needles and Balthazar's right hand is stud with it. In the next shot the doll is full with needles and Balthazar's coat without any.
When Balthazar is tied to the circular electric device in the lab, the two lines that tie his left hand to it are either close together, crossing over, or far apart, depending on the angle of the scene used.
The horn of the subway train entering thee station was that of a diesel electric engine. The horn on the subway train has a higher pitch and sounds different.
If the motorman's view is obstructed (by paper in this case), they would immediately stop the train and remove the obstruction.
When the car is changed into a Ford Pinto, Nicolas Cage mentions the car is a 1973 Pinto, but he is incorrect. It is either a 1974 or 1975 Pinto as proven when looking at the front bumper. The 1973 Pinto had a slim bumper, and the 1974 and 1975 models had a thick 5 mph impact bumper.
When trying to explain to Dave the difference between sorcerers and humans, Balthazar says that humans use only ten percent of their brains. This is a popular urban legend, and is completely false. But Balthazar only asks, "You've heard that humans only use 10% of their brains?" However, he is not affirming the mistaken notion, he's merely asking David if he's heard of it.
When Dave listens to the radio while playing with his "Musical lightning" project, he is clearly standing in a Faraday Cage so to prevent any electric shock. This kind of equipment is also supposed to block any radio signal, which means that his radio would not be able to work as clearly as we can hear.
While it is correct that a Faraday cage would block radio signals, there is no reason an external antenna would not be used to bring a radio signal into the cage. This is done all the time by electrical engineers.
When Balthazar is released from the urn, he is not wearing a hat. In the next scene, he is wearing a hat. But if a sorcerer can change his appearance at will, and change the model of his car in one touch, surely conjuring a hat from the thin air wouldn't be too difficult.
In the car chase sequence, Balthazar's car is a right hand drive car. In the deleted scenes it shows Balthazar and Dave switching seats in the car. This way when Balthazar changes the car to the left hand drive he will be in the driver's seat again.
Before the scene with the mops, Dave picks up the can of soda and as he turns away, the heel of his foot sinks into the floor a little. You can tell it's a set, because the "floor" is actually tile.
The Twin Towers are missing from the New York skyline in 2000.
When 10 year old Dave chases the note in 2000, a 2009-2010 Toyota Camry taxi cab is seen.
When Dave is viewing the New York City skyline from the school bus in the year 2000, Bank of America Tower is visible to the right of the Empire State Building. Construction of Bank of America Tower did not begin until 2004, and it wasn't completed until 2009.
When Dave is explaining his plan to defeat Morgana to Becky the audio doesn't match Dave's lips when the camera is shooting behind him.
When the jar of water falls and breaks on David's lap in the Arcana Cabaña, he is clearly wearing Corduroy pants. After his teacher pulls him outside, and one of the students exclaims, "ew, he peed his pants" the camera zooms in on his pants and they are not corduroy.
When leaving the shop the camera and crane can be seen in the reflection in the shop window.
When Horvath is trapped in the mirror and asks the young man to get Drake for him, as he faints you can see him bump Horvath as he is falling.