[Pokken Tournament] Pikachu, What's This Key?

[Pokken Tournament] - While playing, Pikachu and co. encounter the Pokémon, Klefki, who is able to open up portals to various worlds. 

Pikachu & Co. travel with Klefki through these various worlds, encountering various Mythical Pokémon such as Manaphy, Darkrai, Jirachi and Victini.

Source: Serebii