Continuity mistake: Right before Ben runs over the skunk, he's wearing goggles, but when you see him on the ground right after crashing, he is not.
Continuity mistake: When Despereaux fights the cat in the rat arena, he hides behind a blue ball of yarn. When the cat hits the yarn, causing Despereaux and the yarn to fly in the air, in the next shot, the ball of yarn vanishes and never reappears again.