Continuity mistake: After Buffy finds Morgan's brain, Willow pulls up Morgan's school file on one of the library computers without even touching the keyboard. One moment the monitor is on the desktop, the next it's showing Morgan's file.
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 Stanley is sleeping in his bed as the computer starts to wake him up, his head is turned left under his covers. When the camera cuts to a close up, his head is turned right. (00:06:35)
Continuity mistake: The fish that Harley uses to protect herself from the Joker changes shape and size every shot.