Giles originally forbids Buffy from joining the cheerleading squad, arguing it's a "cult" and a distraction from her sacred duty as the Slayer.
The title of the third episode of (Season 1) is simply "Witch" . Episode Synopsis [S1E3] Witch
For a deeper look into the episode's plot and character development, check out this review: Giles originally forbids Buffy from joining the cheerleading
Buffy and the "Scooby Gang" initially suspect , a fellow cheerleader hopeful, of using dark magic to eliminate her competition. The investigation eventually reveals that Amy’s mother, Catherine Madison , is the true witch. Driven by an obsession with her past "glory days," Catherine used a spell to switch bodies with her daughter to relive her youth. a fellow cheerleader hopeful
The episode features one of the series' first major supernatural twists, where Amy and her mother's consciousnesses are swapped.