Episode 11 of "Buffy, the Vampire Slayer"
s01e11 Out of Mind, Out of Sight
Title: Out of Mind, Out of Sight
Original Air Date: 05/19/1997 on WB
Director: Reza Badiyi
Writer: Ashley Gable, Thomas A. Swyden
Guest Stars: Julie Fulton (FBI teacher), Skip Stellrecht (Agent Manetti), Mark Phelan (Agent Doyle), John Knight (Bud 1), Denise Y. Dowse (Ms. Miller), Ryan Bittle (Mitch), Clea DuVall (Marcie Ross)
Plot Outline:
When a seemingly evil invisible force centers around Cordelia, Buffy investigates and discovers that a student who was ignored by all her classmates, including Willow and Xander... became invisible by their perception of her and she plans revenge on Cordelia because of her popularity.