Continuity mistake: When the evil king's female assistant is "turned into" Odette, and Prince Derek is dancing with her near the end, he puts the locket on her. The chain goes around her hair, and in the next shot, it's under her hair. They were dancing the whole time, so how could she or Derek have pulled her hair out of the chain?
Continuity mistake: When Uberta is telling Derek about the ball, she is standing by a large door. When she says that the ball is only a few friends and their daughters, she is standing right next to the door. When she turns around to tell the short footman that she wants the ball to be big, she and the footman are instantly farther down the hall and not beside the door as in the previous shot.