“Then, you wretched fools... you will learn the error of your ways!”
The Shadow Queen is the true main antagonist and final boss of Paper Mario: The Thousand-Year Door. 1,000 years before the game's events, she arrived in the Mushroom World with hopes of conquering it and making it her own. She was ultimately defeated and sealed away in the Palace of Shadow for 1,000 years, which is where she is throughout the course of the game.
Legend has it that the Shadow Queen simply appeared one day and waged war against the city where Rogueport now stands. She destroyed the city and all who opposed her. The city eventually succumbed to the Queen's rule. She transformed a quarter of the city into the Palace of Shadows, which was her personal base.
With the city under her control, the Queen planned to conquer the rest of the world. She created an army of demonic beasts, the three Shadow Sirens, and the three dragons, Hooktail, Gloomtail, and Bonetail. She used her forces to wreak havoc on any settlement she could.
The Queen then created the Crystal Stars, which held the essence of the heavens. The Queen planned to use the stars to remake the planet in her image. She hid the stars in fortresses and castles across the land. She also created the Pit of 100 Trials to torture those who opposed her.
When the Queen was nearing the peak of her power, four warriors emerged to stop her. They were a Toad, a Goomba, a Koopa, and a Boo. The four planned to steal the Crystal Stars and use their power against the Queen. They gathered the stars and mounted an attack on the Palace of Shadow. They fought through the Queen's entire army, until finally they reached the Queen. The warriors destroyed the Queen's body and sealed her spirit in the foundations of the palace. However, the Queen had cursed the warriors before her death, causing them to prepare for the day when she would return.
The four warriors sealed the palace entrance using the Crystal Stars, and hid the stars in many places all across the land. They also created a Magical Map so that the Crystal Stars could be found after their demise. However, this map was held in a magic chest that could only be opened by a pure-hearted person to ensure that it didn't get into the hands of evil.
The Queen left behind her Shadow Sirens, who began preparations for her revival. They spread a rumor that a great treasure was sealed in the Palace of Shadow so that as many people as possible would try to break the seal.
 Paper Mario: The Thousand-Year Door
After one thousand years pass, the Shadow Sirens begin to prepare for their queen's awakening. They join the Secret Society of the X-Nauts and Beldam, the oldest of the Shadow Sirens, convinces their leader, Sir Grodus, that he will be able to control the Shadow Queen once he frees her.
Beldam finds the chest with the map that reveals the locations of the Crystal Stars. She tells Grodus that one of pure heart is needed both to open the chest and find a suitable host for the Queen. Beldam disguises herself as a merchant and sets up shop in Rogueport. She discovers that Princess Peach is an ideal host, but cannot capture Peach. Grodus sends his X-Nauts to abduct Peach while she is in a back alley.
After Mario gathers all the Crystal Stars, he releases the seal on the Queen's palace and chases Grodus through it. Grodus holds Peach hostage, but Bowser intervenes. Mario defeats Bowser and corners Grodus. Grodus tells Mario and his friends that the Queen needs Peach's body so that she can be fully revived. He summons the Queen and presents Peach as a host. The Queen accepts and possesses Peach. Once reborn, Grodus believes that he can now control the Queen. She is disgusted by his attempts, and ultimately destroys him. After doing this, she notices Mario and his friends and offers to let them be her servants. They refuse, and an enraged Shadow Queen launches an attack on them. The Queen attacks Mario with extremely powerful attacks. Eventually, she becomes invincible, and all Mario can do is wait for the Crystal Stars to appear.
The Crystal Stars appear and travel to their home locations, allowing the people of each area to communicate with Mario. They distract the Queen with their good wishes, allowing Peach to regain control of her body long enough to give Mario all her power. With the combined power of him and Peach, Mario attempts to attack the Queen one last time. Eventually, he defeats the Queen, ultimately destroying her forever. Peach is released unharmed, and all the Queen's followers are no longer a threat. The Shadow Queen is defeated forever, leaving Mario and his friends to celebrate.
 Super Mario-Kun
The Shadow Queen also appears in the Super Mario-Kun manga adaptation of Paper Mario: The Thousand-Year Door's plot.
The Shadow Queen is a ruthless demon that cares only for herself. She cares only for advancing her personal goals, which consist of having the world suffering and making the world look like her. She, unlike several other villains in the series, shows no comical side. She possesses vast amounts of power, and she uses it to kill anyone she wishes. She seems to rule her followers through fear rather than loyalty.
 Power and Abilities
The Shadow Queen, being an ancient demon, is in control of numerous powers. At her full power, she is immune to normal and defense piercing attacks, and can only be made vulnerable with the power of the Crystal Stars. In her spiritual form, she is able to use her hands to drain the health of her enemies. This damages her opponents and pierces their defenses, while restoring her health. In addition to this attack, her arms are also capable of smashing opponents to the ground. Her hands are considered separate enemies. However, whenever they're defeated, it is only temporarily, as the Shadow Queen can revive them the following turn. The Shadow Queen is also able to strike her opponents with lightning, an attack that is difficult to avoid due to its speed and defense piercing nature. When in a dire situation, the queen will often resort to poison, confusion, or allergic toxins. One makes her opponent lose health every turn, another severely hinders opponents' moves, and the last one makes her opponent resistant to status changes, thus making Mario and his partners unable to use Power Lift or a Boo's Sheet.
One of the most harmful attacks of the queen is when she summons many dead hands to come up from the ground and drag her victims down. A even stronger attack with her dead hands is when she uses them to stampede Mario or his partners, which if not protected against can deal 12 damage. Her dead hands can pierce defense. The Queen uses this early in the battle with Mario to attack the audience members and drain their energy to give her full health and power. Her strongest attack consists of sending out black waves of darkness, which hits Mario and his party member. However, this attack takes a turn to charge up before she can use it, allowing Mario to avoid it with Vivian's Veil ability. If not avoided, this attack alone can take off a large portion of Mario's health. The Shadow Queen also has the ability to temporarily raise her attack and defense by noticeable amounts, boosting the power of her other attacks. While not considered to be a battle power, the Queen also holds the ability to possess other beings for her own uses, and seems to be immortal. She holds the abilities of creating many demonic monsters and other spirits to do her bidding.
 Names in Other Languages