Pokemon The First Movie - Mewtwo Strikes Back

A team of scientists create the world's strongest Pokemon, Mewtwo. But Mentwo has it own thoughts and doesn't want to be used as an experiement, so it learns to focus its power and go for revenge on humans by destroying life on earth. Ash and a group of Pokemon trainers are invited by Mentwo to have a battle with it, but they finally discover that the real purpose of Mentwo is to clone their Pokemon. Ash then tries to stop Mewtwo before it is successfull with this plot.