The Pokémon GO Harvest Festival event will run from October 10 to 16 featuring the Pokémon debuts of Dipplin and Hydrapple, you can use 200 Applin Candy and 20 Syrupy Apples to evolve Applin into Dipplin

The Pokémon GO Harvest Festival event runs from October 10 to 16, introducing two new Pokémon: Dipplin and Hydrapple. During the event, players can evolve Applin into Dipplin using 200 Applin Candy and 20 Syrupy Apples, a new item specific to the event. Along with these exciting debuts, there will be special themed activities, bonuses, and a festive atmosphere to enjoy. Whether you’re aiming to evolve your Applin or just soaking in the harvest vibes, this event is a great opportunity to catch some fresh, seasonal Pokémon.

Source: Official Pokémon GO blog and Pokemon.com