A meteor impacts the nation of Equestria, Planet Equis. Tranquility is quickly snuffed out when a poison begins to spread violently. The Princesses cannot combat this unknown threat, as no knowledge of it exists. Help comes from an unexpected source.
To protect his Pokemon from harm Arceus has moved most of his worlds populus to Equestria in hopes that they can live in peace, but peace is often harder to obtain than one might think.
There is a creature in southern land's, that is nearly as old as the nation of Equestria. Once referred as the queen of the forbidden jungle, later imprisoned in Tartarus. Now it's free to roam the land once more.