Xerneas uses its signature move, Geomancy, which increases the launch power of all fighters, but exceptionally raises it for whoever had summoned it.
The horns on Xerneas's head give this Fairy-type Pokémon the power to bestow eternal life. It emanates energy with a move called Geomancy that causes all the fighters to glow. As pretty as it is, this makes everyone more easily launchable. Know when to take advantage and when to lay low.
Xerneas was teased around the time of Pokémon X and Y's release date. Sakurai stated "We have absolutely nothing to announce today regarding Pokémon X and Pokémon Y. Really!".
Xerneas, alongside Victini, are the first Pokémon that can power up the fighters.