1x15 - Friday the 13th: The Series

A homely girl, overshadowed by her prom queen sister, gets hold of a vanity which she can use to bedazzle any boy into falling in love with her. However, as soon as they do, she must then kill them. She eventually takes over her sister's boyfriend and has him hang her up by a noose. Micki and Ryan manage to save the girl, but the younger sister eventually commits suicide along with the boyfriend. The vanity is lost (although it will resurface in the second season episode ""Face of Evil"").