"When this legendary Pokémon's wings and tail feathers spread wide and glow red, it absorbs the life force of living creatures. When its life comes to an end, it absorbs the life energy of every living thing and turns into a cocoon once more."
Yveltal first appeared in X vs. Y: Destruction when it was awoken by Lysandre to satisfy his plans to rid of the ugliness within the world.
Yveltal fought on behalf of Lysandre in order to fulfill this goal, however, when it discovered that Lysandre was in fact just using it to destroy the world and make both Pokémon and humans to be extinct - including Yveltal itself. Angered by this, Yveltal flew to Lysandre in a rage to kill him. After setting alight the Parfum Palace, it is calmed down by Xerneas, before leaving.