12. Season Two: Buffy Grows Up
In the powerful two part episode from season 2, "Surprise" and "Innocence" (which is Joss Whedon's favorite ever episode from the series) Buffy spends the night and has sex with her now boyfriend Angel on her 17th birthday as a great evil known as the Judge is rising in Sunnydale. Little does Buffy know however, that if Angel experiences one moment of pure happiness, his soul will be taken away from him and he will become a mass murdering, cruel vampire once again. At first, Angel who is now Angelus toys with Buffy, pretending that the sex was not satisfactory and as if he was now done with her. Buffy finds this incredibly difficult to deal with until she is given the news of an even worse bombshell. The old Angel, the loving, suffering vampire with a soul is now gone, and he has been replaced by a killing machine that will do everything in his power to make Buffy and her friends suffer. This single moment was probably the first time in Buffy history where the show went from being just great, to completely amazing. These episodes showcased what great actors the cast, but particularly Sarah Michelle Geller and David Boreanaz and from this moment forth, not only was Buffy forced to herself grow up, but the show grew up dramatically too.