Before CGI was everywhere, James Cameron used a clever "low-tech" trick to show two identical characters on screen.

That being said, here are some safer and more legitimate options to consider:

Linda Hamilton’s transformation from a terrified waitress in the first film to a hardened, militant Sarah Connor is a standout, often cited as one of the most believable "badass" female roles in cinema. The bond between Edward Furlong's young John Connor and the T-800 provides the film's emotional stakes, leading to a climax that remains a tear-jerker for many viewers.