Continuity mistake: In the mummy episode, Juliet states that sunlight kills her. However, in the episode before that (Three Monsters), she is shown walking into the sub shop with a calzone box during the day.
Continuity mistake: In episode 25 of season 4, Harper mentions still being in school and even goes to school during the 50's episode to keep her "perfect attendance." But a few episodes earlier, her and Alex both graduate, and even have an apartment. The episodes seem out of order.