After the Cobalt and their Mischief defeat Dark Matter, the Tree of Life comes back to earth. A light descends from the Tree of Life and Xerneas appears, informing the others that it is the Tree of Life.

Soon afterwards, Xerneas comes to the Cobalt's Mischief and informs them that they are the reincarnation of Mew, the ancient Pokémon who battled Dark Matter in the past. Xerneas lets the Cobalt's Mischief touch its horn, enabling him to remember its past as Mew. On the hill with the big tree, the Mischief tells the Cobalt this story he had learnt from Xerneas. The Mischief also reveals that he must leave the world as when he had accepted Dark Matter, the part of it that had come from Mew must disappear along with the Dark Matter. The Mischief then reveals that Xerneas had let him retell this story to the Cobalt before having to depart. At that, the Mischief  ascends into the sky in a ball of light and disappears.

Afterwards, Xerneas lives at the Tree of Life and can evolve Pokémon in the Cobalt's team. Once the Cobalt has connected with at least 600 Pokémon, Xerneas will connect with the team after it is spoken to.

Another: Marriland

Google Docs: https://docs.google.com/document/d/1My5hnJ4XGUmiyp3dV53xchGgj_g48CenoKhEAu_32QA/edit