In the first Pokemon Movie we see that Mewtwo is actually artificially created by Team Rocket and not a naturally occurring Pokemon.
According to this answer there are 2 Mewtwo's and the second female one is still possibly artificially created.
In the trailers for Detective Pikachu (I have not seen the movie yet) we see Mewtwo appear in it. I am wondering if this Mewtwo is one we already know from the anime movies? Or are there now possibly 3 Mewtwo's