Continuity mistake: Notice Marty's hair in the scene when he's playing "Johnny B. Goode." It's quite larger than when he says, some seconds later, "I guess that you're not ready for it yet." That's because when he says that, it's a recycled shot from the original BTTF, whereas most shots showing he's playing the guitar are newly made for BTTF2. However, Marty's hair is considerably longer in the new shots.
Plot hole: Daniel first needs Miyagi's signature (which Miyagi refuses) to enter the tournament. However the rest of the movie focuses on Daniel's signature needed to enter instead. Didn't Miyagi officially need to sign? How did it suddenly switch?
Continuity mistake: When the reindeer gets into the house and runs around, it knocks over a TV set. All of the magazines that are on top of the set come crashing to the ground, including a TV Guide with "Get Ready For A Fabulous February" (or something like that) in big letters on the cover. Interesting since the movie is set around Christmas time.
Continuity mistake: The snowman hits his nose with a hammer, completely bending it in half. In the next shot it is suddenly magically straight again.
Character mistake: In the finals of Video Armaggeddon the compere keeps making comments such as "Jimmy loses a life and starts over in world two", "Laura finishes world two", "Lucas finishes world two". All three times the relevant person is actually in World 1 - Level 3. In Fact at no point are any of the competitors in World 2 and the only time any of them is out of World 1 is when Jimmy uses the warp to access World 4.GameBlade
Continuity mistake: When Wallace races out to get the crackers Gromit is seen spinning in his chair, to the right of the screen is the handbrake in the down position. When the ship blasts off Gromit realises he's left it on and puts it from the up position to the down position. (00:08:30 - 00:09:20)Sanguis
Continuity mistake: When Brian spends his first night in the underground monster world he goes in wearing a shirt and boxer shorts. But a later scene shows him wearing a shirt, pants, and shoes. He then goes back home and is back in his shirt and boxer shorts.