Had an idea of a way to introduce Yveltal's love of chocolate when the MC goes to get her. I assume that the MC carry's some snacks when he goes for the legends so when he goes looking for Yveltal in the desert or death land area he looks and looks but finds no traces of her but ghost type pokemon like Pumpkinboo who could follow him. After a long time the MC decides to take a break and takes out some chocolate to eat and once he opens the package he notices everything got DEATHLY quiet, no wind, no sound and the sun went away. He thinks that he can hear his own heart beating but its the beating of wings getting closer VERY FAST. He looks up and sees YVeltal going straight at him screaming "THATS MINE!" and goes to the battle section. She had just started her new life cycle and is looking for life energy so was ignoring the MC until he brought out that chocolate bar since its been so long she has had any chocolate she goes for him. Once calmed down and tired she still does not want him near her since others have sought her for power so he offers the chocolate for a few minutes of time to show her he is telling the truth that leads to her getting inflated. He promises if she joins him she will never have to worry about getting life energy again and can have access to all the chocolate she can eat.