From Bulbapedia, the community-driven Pokémon encyclopedia.
The Twinleaf Festival (Japanese: フタバ祭り Futaba Festival) is an event in Twinleaf Town that is held every year. It got a brief mention in Barry's Busting Out All Over!.
It was revealed in Three Sides to Every Story! that Johanna was elected to be the chairperson of the most recent festival. She along with Izzy and Cara had organized the events and stalls. Professor Oak had also come as a special guest for the festival in A Faux Oak Finish!.
The Twinleaf Festival also hosts many events including many different contest booths, a singing competition, and the most recent festival featured a battle tournament where the winner could battle Tower Tycoon Palmer.