Deliberate "mistake": While it is established that Angel doesn't age, it's obvious across both Buffy and Angel that David Boreanaz gets older. More unavoidable than deliberate, but still worth noting. Submitted by Cubs Fan
Buffy The Vampire Slayer (1997) - 1 mistake in show overall
Directed by Joss Whedon, starring Alyson Hannigan, Amber Benson, Anthony Head, Charisma Carpenter, David Boreanaz, Emma Caulfield, James Marsters, Marc Blucas, Michelle Trachtenberg, Nicholas Brendon, Sarah Michelle Gellar, Seth Green
Across whole show
Some of these may not have been submitted with enough information to assign them to their proper episode - if you know where they belong, please click the "make changes" link at the top or bottom and then the "change episode" option.
You may also like: Iron Man | Angel | Cloverfield | Friends | Star Wars