This is a case similar to Back To The Future Part II in that Bill And Ted’s Excellent Adventure doesn’t quite qualify for this list despite having Keanu Reeves and Alex Winter play a pair of sequences opposite themselves, but Bill And Ted’s Bogus Journey most definitely counts thanks to the evil robot versions of the eponymous heroes.
Reeves and Winter didn’t exactly need to go to wholly new places for their performances, but it remains a fun pair of dual-role turns (and there is also the bonus of Winter also playing Granny S. Preston, and William Sadler briefly appearing as “English Father” in addition to his more prominent make-up covered character, Death).