Lead a gym.

There are 8 mono-type gyms and a League. Each season runs three months under its own Regulation Set — the rules for which Pokémon and items are legal that season. Beat all 8 gym badges and you unlock a shot at the League. Gym leaders are expected to stay active: go quiet for 14 days with no word to staff and your gym reopens to other applicants. Your team also has to stay legal under the current season's Regulation the whole time you hold the post. Read more on the gyms & league wiki page.