Never Kill A Boy On The First Date - S1-E5
Other mistake: In the famous scene where Buffy tells Giles, "If the Apocalypse comes, beep me," she grabs her pager from out of shot. Trouble is, she's standing in the middle of her hall and there's nowhere she could have picked the gadget up from. (00:21:00)
Clash of the Megazords - S1-E29
Other mistake: When TJ goes to get the Phantom Ranger's ruby, he is standing on top of the battery pack on the Turbo Megazord. There are no other places for him to stand. After he destroys and knocks off the battery pack, in the next shot he is still standing in the same place, but there is nothing for him to stand on.
Other mistake: As Kai's squadron are approaching The Fore Shadow, the ship begins to fire its massive web like plasma waves at the planet, and fires over and over continually. Except in close up shots as Kai's squadron are flying around it. Like it completely stops firing in closes ups, though when cutting away suddenly blasts are close enough to it that they would have been coming out during those close ups. (00:03:05)