Baywatch (1989)

S4E16 Mirror, Mirror

A captivating free-spirited woman named Mattie and her more ordinary twin sister, Gwen, show up at the beach, both competing for Mitch's attention. Unbeknownst to Mitch, Mattie and Gwen are actually two sides of the same person, struggling with split personalities. As the situation unfolds, Mitch finds himself in serious trouble when Gwen's alter ego, Mattie, takes a dangerous turn and threatens him.