Yveltal

Vveltal is a legendary Pokemon from the Kalos region, who was well known for its ability to absorb the life force from living things when its life span was about to end. About 800 years ago, when Yveltal spreads its ominous wings, it engulfed the land of Kalos with darkness. Many people and Pokemon fall one by one throughout the land dueto Yveltal absorbing the life force from them. Then after absorbing enough life force from the living things, Vveltal took to the sky, and disappeared to an unknown location.

When its was near the end of it's 1000 life span, it absorbed the life force from living things in order to charged its own energy. When it was at the end of its life span, Yveltal turns itself into a cocoon. Then Team Flare eventually found Yveltal while it was sill a cocoon at the time. They brought it to Team Flare Secret HQ, where they used its stored energy for their own plans.

However, When Serena/Calem went into Team Flare's lab in order to stop their plans, Yveltal was finally awakened from it's cocoon thanks to Lysandre's plan. After Yveltal was awaken, Serena/Calem battled it and would eventually caught the legendary Pokemon. It would later fought Lysandre alongside Serena/Calem, and would eventually won the battle against him.