Beware the Third Wish - S1-E31
Continuity mistake: The Wicked Wisher throws giant exploding coins onto the field TJ is on, as TJ runs towards the WW. The giant coins remain on the field after they explode, yet when TJ reaches the top of the field, there is no sign of the coins, or their remains.
Continuity mistake: When Sheila Carlisle has hanged the dead head up on the wall of Eugene's office, they are all looking at it and the eyes are looking straight in to the room. Later in the episode, the eyes are looking more to the right.