7. Season 5: Buffy has a Sister?
Season 5's opening episode perhaps brought the biggest shock and plot twist we had ever seen to the show. In fact, arguably, this is the single most surprising and baffling moment from any TV series. Buffy was an only child, but suddenly a bratty teenage sister suddenly appears in her life and we as the audience are supposed to accept this. I guarantee that there were probably a lot of the audience who simply gave up on the show at this point... however, if you did, you missed out of the greatest story ever told in a season of television. The idea to introduce a sister for Buffy completely changed the character, whilst allowing her to still remain the Buffy we all knew and loved. Buffy with a sister forces her to be both more mature, and also shows us an entirely new side of her that was great to get to explore. In fact, it is difficult to imagine Buffy not having a younger sister now... it became an integral part of the show and worked so seamlessly. Credit must go to the writers for being brave enough to pull this off, and especially brave enough to not reveal what Dawn actually was straight away. In the episode after this, entitled "Real Me" we see the world from Dawn's perspective, and all the characters act as if she had been there for years when we know that she simply had not. This is the most confusing plot development from a television series of all time, but more than this, this development actually had one of the best pay offs ever seen on TV before or since.