Continuity mistake: When Max is running out of the school after successfully becoming cool. We see his friend with the orange mohawk at least twice. Once hanging from a statue, and another where he's reaching out from a school bus. These two shots are really close together so there is no way that he could have moved that quick.
Continuity mistake: After you hear Godfather Drosselmeier off screen say, "That's not amazing!" the camera then cuts to him walking in the door to the living room. Beside the door on a mantel is a large round vase with a bushy green plant in it, and there is a picture frame on the wall with a red picture in it. Then it cuts to a close up of Drosselmeier saying "I'll show you amazing." Suddenly the vase is much smaller and shaped like a cup, the plant is now flowers, tulips by the looks of them, the picture in the frame on the wall turns blue with clouds in it, and a stand up picture frame and green box suddenly appear on the mantel next to the vase.
Continuity mistake: In the lunchroom when the boy gets tripped, a bunch of the food flies out of the bowl in the slow motion shot. When the bowl lands on Steve Guttenberg's head, it's full of food.
Continuity mistake: When Angus and Yellow reach the lake, Angus's face is tore up pretty bad, but after they cross the lake and go to the building on top of the mountain his face is almost completely free of any injuries.