The Shadow Queen is the true main antagonist and the final boss of Paper Mario: The Thousand-Year Door and Hello yoshi Brawl season. One thousand years before the game's events, she arrived, hoping to conquer the land. She was defeated and sealed away in the Palace of Shadow, where she remained for the last millennium and throughout the course of the game. After one thousand years have been passed, Beldam plans to revive her through manipulation of the X-Nauts.
Mario and his friends enter the Palace of Shadow, her current location, to destroy her and save Peach, but in the end, Grodus provides Princess Peach as a vessel for the Shadow Queen and she possesses her, forcing Mario and his friends to defeat the possessed Peach. Eventually after the queen exits Peach's body due to being uncomfortable and is weakened by the power of the Crystal Stars, she is defeated and sealed again by Mario and his partners for good. In Hello Yoshi fanmade, the queen also possesses Yoshi's body (Paper Yoshi).