In Buffy the Vampire Slayer's sixth season, longtime protagonist Willow Rosenberg becomes addicted to magic and transforms into one of the show's Big Bads. It's a controversial plotline for several reasons, but the most concerning is that it helped to popularize the trope of heroic female characters suddenly losing control because of power, grief, or addiction, and then becoming — however temporarily — a villain.
Source：https://www.cbr.com/buffy-star-wars-wanda-daenerys-trope/
