“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. She is an ancient 1,000-year old demon. She came to the Mushroom World so she could conquer and rule it. She was sealed before the events of the game, and the entire story revolves around her revival and eventual death.
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 Shadow Palace. 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.
The Queen had cursed the warriors before her death, causing them to prepare for the day when she would return. They sealed the palace entrance using the Crystal Stars, and hid the stars where only a pure-hearted hero would be able to obtain them.
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 Shadow Palace 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 mistress' 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 says that the queen needs Peach's body so that she can be fully revived. Grodus summons the Queen and presents Peach as a host. Grodus thinks that he can control the Queen, but she destroys him. The Queen offers Mario the choice of becoming her servant, but he refuses. 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 take control long enough to give Mario all her power. Mario is now able to damage the Queen, and he battles her. Eventually, he defeats the Queen, sealing her for good. 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, 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 which are seemly demi-godly like. At her full power, she is completely invincible (even attacks that pierce defense don't work on her), 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 life force of her enemies. This damages her opponents while at the same time giving her energy and also pierces their defense. 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, the Shadow Queen revives them a turn later. The Shadow Queen is also able to strike her opponents with lightning, an attack that is difficult to avoid due to how fast it is implemented and pierces Mario and his companion's defenses. 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 makes her opponent so incapacitated that he or she will often attack their own allies or miss an attack all together, 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 upon dozens of demonic hands to come up from the ground and drag her victims down to be issued a large beating. 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 demonic queen used this early in the battle with Mario to attack the audience members and drain their life force to give her full health and power. Another very harmful attack is when the queen uses one full turn to build up energy and then release demonic energies at her enemies. This attack alone can take off a large portion of Mario's health. Her strongest attack consists of sending out black waves of darkness, which hits Mario and his party member, but this attack takes a turn to charge up before she can use it, allowing Mario avoid it with Vivian's Veil ability. The Shadow Queen also has the ability to temporarily raise her attack and defense by noticeable amounts, and when the queen has her attack and defense raised, she is able to do the Megawave, a special and powerful attack reminiscent of Mario's own Supernova created when the queen charges and boosts her attack and defense power by 3, dealing 17 damage, and, if the player is using the P-Up, D-Down badge, the damage can be devasting, dealing up to 20 (if the player uses 3 P-Up, D-Down badges). While not considered to be a battle power, the queen also holds the ability to possess other beings for her own uses. The Queen seems to be immortal. She holds the abilities of creating unlimited amounts of demonic monsters and other spirits to do her bidding.
 Names in Other Languages