Pokemon Sun & Moon: Battle Tree/Pokemon League details

The Battle Tree- Where strong opponents await! Somewhere in the Alola region, you’ll find the Battle Tree: a place where those Trainers who have completed their island challenge—or who are strong enough to have done so—battle one another. All of the Trainers you can encounter at the Battle Tree are strong. It seems you might even encounter two battle prodigies from the Kanto region...

At the Battle Tree, you can scout an opponent you’ve won against so they can partner with you in future battles. You may even be able to scout some familiar faces...

Pokemon League: In the regions that have served as the setting for your adventures in the Pokémon series so far, the ultimate stage for battle has always been a place called the Pokémon League.The Pokémon League is where the Elite Four—four Pokémon Trainers with powerful Pokémon partners—and the Champion, who reigns as the top of all Trainers, await challengers. A challenger who defeats the Elite Four and the Champion will be hailed as the new Champion of the Pokémon League.In the Alola region, the setting of Pokémon Sun and Pokémon Moon, there is no Pokémon League yet—but it seems that there are plans to construct one on the peak of a certain mountain.After the growth you achieve through completing the island challenge, will the day come when you also take on the Pokémon League to become the strongest Pokémon Trainer?