Yveltal appeared in Diancie and the Cocoon of Destruction as a being of destrucion where it destroyed the whole forest following the laws of nature. Later it went on deep slumber. When thieves fighting over for Diancie in an underground pool where Yveltal is sleeping caused disturbance in the forest, Yveltal woke up and started to destroy the whole forest again in anger. Diancie tried to stop it but couldn't until Xerneas granted her energy. Due to that Diancie was able to mega evolve into Mega Diancie to create large diamond. Later the thieves Argus Steel and Millis Steel use their airship to fire missiles on Yveltal, but Yveltal avoid them so easily. It flew towards the thieves airship, grabbed it, and turned them into stone. Xerneas reappeared and battling it, and then Xerneas uses its Fairy Aura to calm Yveltal down halting its rampage. After that Yveltal went away flying peacefully.