The She-Creature | 1956
When Andrea Talbott, the assistant to carnival hypnotist Carlo Lombardi, is herself hypnotized, the results are not positive. Lombardi somehow zaps Talbot's soul into the body of a prehistoric creature that lives below the waves. Lombardi commands the creature to the surface and uses her to destroy those who stand against him. Eventually, though, Talbot figures out a way to take back control of her will and fight her twisted employer.