9. 'The Wish' (Season 3, Episode 9)
The prevalence of magic in the Buffyverse allows the show to examine its lead character's powers from multiple angles: One episode turns her into a powerless Southern belle via a magical Halloween costume; another has her temporarily losing her powers, requiring those around her to step up and help. In “The Wish," Buffy's enemy-turned-friend Cordelia, reeling from a breakup with fellow Scooby Xander, wishes the slayer had never come to Sunnydale. Lucky for her, she' s just met a new girl in school, Anya – who would figure in the show more prominently later – and voila! The alternate universe depicted is something of an It's a Wonderful Life moment for our heroine, with the town overrun by vampires who are completing a “factory" where blood is systematically sucked from humans. (It's then poured directly into wine glasses for easy on-tap consumption.) Willow and Xander are now vamps and Angel is imprisoned until a much darker version of Buffy rides into town to save the day. Lots of fun scenery-chewing ensues before we're whisked back to the comparatively sunny “real" version of Sunnydale.