Kyurem will act as the misunderstood Poke-villain, wreck havoc and all that. The Musketeers will fight and defend Pokemon and territory from it. Keldeo will be similar to Shaymin and bond with Ash & crew and save the day and the misunderstanding between Kyurem and his Musketeer group. Then they will go after the "real" human villain of the movie, in which they will all fail until Kyurem goes into his alternate forme and kicks @ss.
Its fun to predict Pokemon movies, because they're so predictable.