Hoopa no Odemashi Daisakusen!!

A series of six anime shorts for the XY series, leading up to the release of Hoopa and the Clash of Ages. They star Ash Ketchum and his Pikachu as they deal with trouble started by the Mythical Pokémon Hoopa.
The shorts originally aired weekly on Oha Suta from April 23, 2015 to May 28, 2015. English versions of all six shorts were available on Pokémon.com starting on December 11, 2015.
(Source: Bulbapedia)