Complex sentence: He also participates in the Unova League, where he makes it to the Top 16-here, he and Ash have an intense 3-on-3 battle, in which Ash defeats him.
Split into simpler sentences: He also participates in the Unova League, where he makes it to the Top 16. Here, he and Ash have an intense three-on-three battle in which Ash defeats him.