https://www.gamespot.com/articles/special-pikachu-giveaway-for-pokemon-sun-and-moon-/1100-6453431/

Nintendo has begun distributing another free Pokemon for Sun and Moon. Beginning today, players can add a special Pikachu wearing Ash's hat to their teams.

In honor of the series' 20th anniversary film, Pokemon the Movie: I Choose You, Nintendo is giving away six different Pikachu, each of which sports one of the caps that Ash wore throughout the anime. Additionally, each Pikachu also comes with a slightly different moveset that reflects the attacks it used at that point in the series.