Bringing Prof. Oak’s letter and a Gracidea Flower, Marley encountered Shaymin on Route 224, and brought it with her into the Distortion World. There, Shaymin participated in the great battle between the legendary Pokemon, and even transformed from its Land Forme into its Sky Forme in an attempt to stop Giratina from returning to the real world. It decided to stay with Marley after the battle.
