Pokémon the Movie: Volcanion and the Mechanical Marvel

The Mythical Pokemon Volcanion suddenly appears in front of Satoshi and Pikachu in the Azoth Kingdom. Volcanion calls out for Magearna, saying that it's come there to rescue it. Just who is this "Magearna" that Volcanion seems so eager to help!? Alternative title: Pocket Monsters XY & Z: Volcanion to Karakuri no Magearna; Pokémon the Movie: Volcanion and the Mechanical Marvel; Volcanion and the Mechanical Marvel