Hoopa and the Clash of Ages- Pokemon the Movie

Aiming to become a Pokémon Master, Ash and his friends continue their journey. While they sit around in a Pokémon Center in the desert eating donuts, a mysterious ring suddenly appears behind them. What's more, a hand emerges from within the ring and tries to take their donuts! "Wait!" Ash yells as he and Pikachu grab hold of the hand, but he and Pikachu both get pulled into the ring. As they disappear within the ring, Serena, Clemont and Bonnie, left behind, are quite taken aback… ?????~!? Odemashi-! Suddenly bursting out of the ring, Ash and Pikachu are bewildered by the sudden change of scenery. "Hehehe, surprised are you?" "What are you?" "Hoopa!" Far in the distance there is a tower. It appears that Ash and Pikachu travelled through the ring all the way to the goal of their journey, Dessel City, in an instant. The never before seen Mythical Pokémon, Hoopa. What could it be? What sort of power do its rings hold?