Yveltal is the Pokémon that once caused the "Great Destruction", which annihilated all life in the Kalos region. It is known as the "Destruction Pokémon" and is said to steal all life away. After it destroyed everything,
Yveltal turned into a "Cocoon of Destruction", in which form it still sleeps today.
Yveltal was reawakened when the bandits disturbed it and it began to cause havoc in the Alearth Woods once again.
Xerneas intervened and
Yveltal was driven off.