 Producers and the director, Michael Haigney (qv) stated that there  was a lot of trouble having to match the animated lip movements. The  script was written twice to try and make sure that all the dialog  matched up. They also said that they were very happy that Mewtwo was  a psychic Pokémon, because he would converse using his ability and  so there were not many times where his mouth was moving, so they did  not have to work around making the dialog match his mouth movements.