Shadow Queen

"Then, you wretched fools... you will learn the error of your ways!"

- Shadow Queen

The Shadow Queen is the true main antagonist and the final boss of Paper Mario: The Thousand-Year Door. 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. The Shadow Queen is also the only final boss in the Paper Mario series to not have any official artwork.

Background
It is said that the Shadow Queen simply appears one day and wars against the city where Rogueport now stands. She destroys the city and all who opposes her, forcing the remaining inhabitants to surrender to the Queen's rule. She transforms a quarter of the city into the Palace of Shadows, which is where she resides in for the majority of the game's story. With the city under her control, the queen plans to conquer the rest of the world by creating a variety of monsters, including the three Shadow Sirens and the three dragons who end up becoming her pets.

Upon doing this, the Queen creates the Crystal Stars, which hold the essence of the heavens and she plans to use them to remake the planet how she sees fit. The Shadow Queen hides the stars in fortresses and castles across the lands, and creates the Pit of 100 Trials to torture all who oppose her.

When the Queen is near the peak of her power, four heroes (a Toad, a Goomba, a Koopa Troopa and a Boo) emerge to stop her by stealing the Crystal Stars and using their power against her. They gather the stars, invade her Palace, and attack the Queen, destroying her body, although her spirit survives and is subsequently sealed in the foundations of the palace. Upon death, however, the queen curses the warriors, forcing them to take precautionary measures.

Paper Mario: The Thousand Year Door
The Shadow Queen's role in the story is short, however, the game's main plot is about the resurrection of the Queen.

When Mario and his friends gather all seven Crystal Stars and follow Grodus with Peach to the room where Shadow Queen's spirit rests, Grodus summons the Queen and presents Peach as a vessel for her, whom the queen then possesses.

Now reborn, the Shadow Queen almost eradicates Grodus for thinking he could control her. The Queen then notices Mario and his friends and offers them the position of her servants, so they wouldn't die. They refuse, leaving the Shadow Queen in anger. Offended because they refused her, she attacks the party. At some point of the battle, she leaves Peach's body, because it was uncomfortable and blocked her power. She assumes her real from, that is, unfortunately, impervious to Mario and his friends' attacks.

Once the Crystal Stars travel to their home locations, allowing the people of each area to communicate with Mario, the Shadow Queen becomes distracted by their good wishes, which allows Peach to regain control of her body long enough to give Mario all her remaining power. Restored, Mario and his partners battle against the Shadow Queen once again, now able to damage, defeat and seal her forever. Once she is sealed, she leaves the world forever, and Peach takes control of her own body once again.

Super Paper Mario
In Super Paper Mario, the Shadow Queen cameos as a doll in one of Fort Francis' rooms that are filled with Paper Mario: The Thousand Year Door character dolls and posters.

Super Mario-Kun
The Shadow Queen also appears in the Super Mario-Kun manga adaptation of Paper Mario: The Thousand-Year Door's plot. As with most characters in the manga, she displays more of a comic side.

Powers and abilities
The Shadow Queen is an immortal demon, having survived for a full thousand years while being sealed in the Palace of Shadow. She can also possess other people, and has a variety of magic at her disposal, which she uses to create powerful creatures and objects such as the three dragons and the Crystal Stars.

In battle while in her true form, she is immune to normal and defense-piercing attacks, and can only be made vulnerable with the power of the Crystal Stars. In her true form, she is able to use her hands to drain the health of her enemies and pierce their defenses. They are are also capable of smashing opponents to the ground, and are considered separate enemies that can be targeted individually. Whenever they're defeated, the Shadow Queen can revive them the following turn. The Shadow Queen is also able to strike her opponents with lightning that pierces her target's defences. When low on health, the queen will often resort to attacks that induce poison, confusion, or allergies that prevent status changes.

One of the Shadow Queen's stronger attacks is the use of several shadowy hands that come up from the ground and drag Mario or one of his partners down into the shadows and damage them with several attacks or stampede them for heavy defense-piercing damage. The queen will also attack the audience members with these hands to drain their energy to restore her to full health and power. Her strongest attack is a series of dark energy waves that hit Mario and his partner for heavy damage, but this attack takes a turn to charge up, allowing Mario to avoid it with Vivian's Veil ability. Additionally, the Shadow Queen also has the ability to temporarily raise her attack and defense by 3.

Personality
The Shadow Queen is a demon who cares only for herself and her aspirations, particularly conquering the world and remaking it in her image. She seems to rule her followers through fear rather than loyalty, as she often uses power to intimidate them. She also acts like she is superior to everyone, challenging Mario and his party, just because they look weak.

Some of the Shadow Queen's speech and behavior vary somewhat between the Japanese and English versions of the game. In the Japanese version, she speaks in a considerably more down-to-earth manner. For example, when she sees Mario and his party members, she describes them as looking "agreeable", and when she offers them a second chance to serve her, she says if they agree she will "let bygones be bygones." In the English version, she speaks more formally, and is more condescending, backhandedly describing Mario and his party members as looking weak but possibly useful.

Appearance
While possessing Peach, the Shadow Queen looks like the princess: her skin turns darker, her dress becomes black with white details, and she now wears a cloak (black with white details as well). Her crown and her jewelry take new shape and are red now. She also takes a more cruel expression, instead of Peach's sweet one.

On the other hand, her true form is of a purple demon. She has a spiralated body, with "stars" in it. She wears a crown, and her hair is a grayish purple tone. She has large hands that aren't connected to her body.

Trivia

 * It is possible to accept the Shadow Queen's offer to join her side. Doing so will result in a message stating that she has engulfed the world in "her foul magic", and cause a Game Over.
 * Unlike every villain capable of kidnapping Princess Peach in the extended Mario series, the Shadow Queen is only capable of possessing her.
 * It is possible that the Elder Princess Shroob could be a reference to the Shadow Queen, as they both do not appear before their role as the final boss. Along with that, a smaller counter part of each (Beldam being the Shadow Queen's and Princess Shroob being Elder Princess Shroob's) is constantly seen before the final boss reveals herself.