The Shadow Queen is a fictional demon in the video game Paper Mario: The Thousand-Year Door. The tale states that the Queen suddenly appeared one day in the city of Rogueport. Her army of demons domination of the planet was certain. However, four heroes rose and decided to wage battle against her army. They used four of the Crystal Stars that the Shadow Queen created to destroy her body and seal her behind the Thousand-Year Door. Before she was sealed, the Demon cursed the four heroes, stating that when they let go of the Crystal Stars, they would be trapped within a chest for all eternity.
After hundreds of years, the battle that occurred so long ago started to become nothing but a mere legend. After 1,000 years had passed, the three Shadow Sirens knew that the time to release their queen was soon to come. The three of them convinced the X-Naut army to help them find the scattered Crystal Stars to open the door. The X-Naut ruler Sir Grodus thought that if he could open the door and sacrifice a princess to the demon, he would be able to rule the world.
After Sir Grodus managed to open the thousand-year door, he offered Princess Peach to the demon, who soon later possessed the princess. Mario will then have to fight the princess. During mid battle, Peach will temporarily regain control of herself and give the last of her power to Mario. Now Mario will be able to defeat the actual Shadow Queen, and seal her once again. But the Shadow Queen has many twists.
According to one of the game's characters, Hooktail, Bonetail, and Gloomtail (three bosses in the game) are her pets. She is known to be a very hard boss with high HP, devastating attacks, and 3 phases.