Our heroes - or mainly, Ash - compete in a contest at Cameron Palace to earn the title of the "Guardian of the Aura". Little do they know that the legend of Sir Aaron may not be as it seems, and that the staff that's been handed down from generation to the next actually holds within it a Pokémon Lucario - an apprentice of Sir Aaron himself.
The movie's plot if pretty good, the art is the usual level of Pokémon movies, and I really liked this film; it was eventful, didn't repeat itself (something that happens in children's movies/shows all too often to underline the meaningful points in the plot), and the inner struggle and emotions of people and Pokémon alike were easy to sympathize with. The story was also coherent, and there weren't weird twists or errors. Even Team Rocket fit in very well in this one.
Mew makes its second appearance here. I miss the voice it had in the first movie, but what can you do. Also, I don't know why, but May didn't look or sound like herself in this one (maybe the voice actor changed, and her look at the ball was a lot different from her usual traveling outfit).
All in all a must-see for Pokémon fans. One of the best movies in the series, for sure!