Revealing mistake: As Kevin is flying off the front porch on the toboggan, you can see the small wheels mounted on the bottom of the sled to aid in its "jump". (00:25:30)
Revealing mistake: When three of the turtles are playing Trivial Pursuit and Leonardo runs in to announce Splinter is alive, you can see a wire coming out of Raphael's shell. I guess it's for the animatronic head, but it's visible. (00:59:30)
Revealing mistake: At the end, when the train destroys the time machine, right at the moment when it hits you can see a small explosion, which was used to trigger the destruction of the time machine. (01:43:03)
Revealing mistake: In the hotel meeting scene, the Grand High Witch tells the witches they can take their wigs off. When we see the newly bald witches, it is particularly obvious that only the foreground witches are ladies with bald caps - the rest of the witches are bald men. (00:30:10 - 00:31:00)
Revealing mistake: Right after Xayide dies we see a shot of two monsters. One of the monsters explodes and the particles from the explosion hit the other monster making it break in half before it explodes itself. (01:15:25)
Revealing mistake: There are a couple times you can see the tape that marks where the actors are supposed to stand in the shot. In the beginning, when Bobby and his brother walk in on Ernest trying to get a cleaning machine to work, look on the floor and you will see some tape in the shape of a T. Bobby will move his feet to the T. Also when a criminal begs for Nash's help because he killed someone, and Nash walks forward, look on the floor to see another tape T, and what do ya know, Nash stops right on the T.
Revealing mistake: When "Krebbs" the koala is discussing with his other friends in the cell. If you look closely, you can notice a blink in the outline in the "Krebbs" nose. It's a clear ink & paint mistake of the blur line.
Revealing mistake: When Tracy and Kid escape the explosion, the stair and rail wobble, revealing they're a prop.
Revealing mistake: When Webby and the others are standing outside of the window watching Scrooge pace back and forth in anger, she casts no shadow on the patio. This is revealed when she moves left at one point. (00:28:50)
Revealing mistake: When the car crashes into the tall display of tennis balls in the store, there's a dummy on top of the car dressed up in the same clothing as Ben.