Watch Pokemon: Power of One (1999) full movie in English.
Other title: Pokemon: The Movie 2000
Pokemon: Power of One storyline: An evil genius in a flying fortress is trying to kidnap the birds of the fire, ice, and lightning islands in hopes of luring the sea power, Lugia, and controlling the world. Ash and his friends, in the process of carrying out an island tradition that requires visiting those three islands, discover the plot and try to stop it. Even the comic villains, Team Rocket, turn good and help out in the end against the threat of world destruction. And Pokemon assemble from all around the world in case they can be of help (but they end up helping only the merchandising).
More infor: IMDB, Wikipedia