Theory: Princess Shroob Usurper

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Status High Consensus
Author Ymcan64
Date of creation November 2, 2023


Princess Shroob and the Shroobs from Mario & Luigi: Partners in Time kept the pieces of the Cobalt Star separate so the younger Princess Shroob would usurp the throne from her older sister.


  • Argument 1: After the Cobalt Star is shattered, its pieces are scattered to various places. Two of these are kept by creatures that are adjacent to the Shroobs, Swiggler and Petey Piranha, with Peach being kept by them as well and holding a third. At no point do the Shroobs attempt to reconstruct the Cobalt Star and instead it seems they are keeping the pieces in their possession.

  • Argument 3: There are two large, unique Shroob UFOs in Mario & Luigi: Partners in Time. One is the Shroob Mothership seen at various points through the game and the second one is smaller and found in Shroob Castle. It is smaller and never used by any Shroobs, only by the Mario Bros. to fight against regular Shroob UFOs. The second unique UFO may have belonged to the younger princess and the Mothership to the elder princess, with the younger princess taking it over afterwards.

  • Argument 4: The Elder Princess Shroob is shown to be abusive to the Shroobs during the battle against her such as when they bring her a drink, as opposed to the younger princess when the Shroobs perform similar actions for her. This may be why the Shroob people are cooperating with the younger princess's usurpation plot.


Note as of 11-12-2023: The idea of this post is somewhat based on and inspired by this old GameFAQs thread I read many years ago. I had forgotten where exactly I had read this and thought it was old YouTube comments or some other place, but found the thread again today. So credit to wiiking96 for the inspiration.

The Shroobs are an alien race from the Mario series and the main antagonists in Mario & Luigi: Partners in Time. Due to their planet dying out, they sought a new home and invaded the Mushroom Kingdom in the time when Mario was still a baby. The rulers of this species are two characters with the same name, the two Princesses Shroob. They are sisters, though the existence of the elder sister is kept a secret for most of the game. The elder Princess Shroob acts as the secret final boss of Partners in Time and her existence is foreshadowed at various moments throughout the game. The relation between the two Princesses Shroob from the perspective of the younger sister is not explored a lot in the game however, likely in part to keep the twist intact. However, as this theory will argue, the younger Princess Shroob and her people might also have motivations to not acknowledge the existence of her sister for most of the game.

Pieces of the Cobalt Star

One of the first places the Shroobs attacked when they arrived on earth was the Mushroom Castle. Around the same time as this, a time machine from the future with Princess Peach, Toadiko and Toadbert arrived in the castle. According to Peach just before the true final boss, immediately upon exiting the time machine, the trio was greeted by the two Princesses Shroob. The elder princess attacked, but Peach grabbed the Cobalt Star powering the time machine. She trapped the elder princess inside the star, upon which it shattered in six pieces. Peach was then captured by the younger princess Shroob and taken away, while Toadiko was brought to Toadwood Forest by the Shroobs and Toadbert was swallowed by Yoob at some point.

The main quest of Partners in Time involves retrieving the pieces of the Cobalt Star, as they were scattered to various places at some point after the Shrboos’ initial take-over of the Mushroom Castle and Toad Town. The locations we find some of these pieces in offer the first leg of the theory. But first, a rundown of where the pieces are found and how they likely ended up there:

  • Inside a treasure chest in Bowser's Castle. The piece was likely brought here by Baby Bowser's minions, as Baby Bowser identifies it as his treasure after the fight with Swiggler. They may have grabbed the piece from the Mushroom Castle, as he was in it around the same time when Peach, Toadbert and Toadiko arrived from the future.
  • Held by Swiggler in the Shroobs’ Vim Factory. The piece was likely put there by the Shroobs, as Swiggler is important for their infrastructure, since it creates the fuel for their UFOs.
  • Held by Petey Piranha, who lurks in the Gritzy Caves. Given that Petey Piranha was likely engineered by the Shroobs and they feed Peach to it at one point, it is likely the Shroobs put the Cobalt Star shard in Petey as well.
  • Sealed in a glass sphere in the Star Shrine. It is unclear how a part got to this location, given the Shroob presence in the area is low and none of the other characters in the Mushroom Castle at the time are known to have gone to the Star Shrine prior to the Mario Brothers collecting the piece.
  • Held by Toadbert, who likely grabbed a piece when the Cobalt Star first shattered.
  • Held by Princess Peach, who likely grabbed a piece when the Cobalt Star first shattered.

On the whole, it thus seems the Cobalt Star pieces were taken and moved by those who were in the Mushroom Castle at the time. Peach and Toadbert likely took their pieces to stop the elder Princess Shroob from being reformed and Baby Bowser took his piece because he thought it was a shiny treasure. But why would the Shroobs take two pieces and keep them knowingly apart from each other? Would they not want to free their monarch and so keep the pieces together? Of note is also that Peach was captured by the Shroobs and she is kept apart from the other pieces as well for the most part (except for the time she spent in Petey Piranha’s belly). It does give the impression that they are trying to keep the pieces apart deliberately, but as to why this might be the case, further evidence needs to be examined.

The attitude of the younger Princess Shroob

For most of Partners in Time, the younger Princess Shroob is thought to be the leader of the Shroobs. This is to keep the existence of the elder Princess Shroob a secret from the player, but the actions and words of the younger Princess Shroob seem to show she also considers herself the singular leader of her people. As mentioned before, she does not acknowledge the existence of her sister for most of the game. Instead of seeking her sister’s liberation also, she organizes a grand ceremony at the Koopaseum where Peach is fed to Petey Piranha. This seems to be an execution ceremony celebrating the Shroobs’ successful conquest of the Mushroom Kingdom, where the old kingdom is symbolically killed off.

Mario, Luigi and their baby selves go on to defeat Petey Piranha not long after this, but do not find Peach inside his belly. Instead, she was spat out and moved to Shroob Castle. The younger Princess Shroob also impersonates Peach. She is found by the four Mario Brothers and brought to the present, though later kidnapped again by Bowser and brought to the past. Kylie Koopa speculates that this was deliberate after this is found out aboard the Shroob Mother Ship:

“You took that dame through a time hole to the future Mushroom Kingdom? Are you saying you think that was Princess Shroob’s plan all along? Talk about a twist! Yeah, she sets herself up as Princess Peach and infiltrates Peach’s Castle in the future… What she’s really after… is the chance to conquer the Mushroom Kingdom of your time, too! The gall of this gal!”
Kylie Koopa, Mario & Luigi: Partners in Time

So her celebration of the successful conquest of the Mushroom Kingdom in the past leads directly into a plan to start conquering the Mushroom Kingdom of the present. The younger Princess Shroob is power hungry and has her sights set on even more conquest, instead of freeing or even acknowledging her sister. A quote from the princess herself just before she is fought sums the attitude up quite well:

“This kingdom is mine!”
Young Princess Shroob, Mario & Luigi: Partners in Time

Contrast this to how the elder Princess Shroob describes her goals for conquest after her defeat:

“One day, the Shroobs will dance on the buried remains of this pathetic kingdom…”
Elder Princess Shroob, Mario & Luigi: Partners in Time

She seems to see it as more of a shared goal, while her younger sister sees it as her own ambition as the sole Shroob ruler

This attitude can also be seen in the design of the Shroob Castle. It is only after the elder Princess Shroob being sealed away, that the Mushroom Castle was converted into Shroob Castle. On the ground floor of the castle, a large statue of the younger Princess Shroob is present. However, this statue pales in comparison to the identical but gigantic statue of the younger princess that stands atop the castle. And inside, on one of its highest floors, we find a room with a single throne. Not two. The castle is clearly solely designed for the younger Princess Shroob, with no design hints of the elder Princess Shroob anywhere.

A related aspect is the UFO that the younger Princess Shroob uses as her vehicle at various points through the game: The Shroob Mother Ship. It is the largest and most dangerous Shroob UFO that the Shroobs seem to have in their arsenal, but it is not the only unique and large UFO in the game. A second one is found on the second floor of Shroob Castle and it bears several design similarities to the Shroob Mother Ship, but is noticeably smaller and is never used by the Shroobs. It is just laying around in the castle, allowing the Mario Brothers to take out several smaller Shroob UFOs. The intended occupant seems to be missing or not using this UFO. Perhaps this then is the UFO actually belonging to the younger Princess Shroob, while the Mother Ship she pilots actually belongs to her elder sister, given the elder princess is presumably considered of higher authority than the younger one. This would explain the existence of the smaller, unique Shroob UFO which is nonetheless still similar in design to the Mother Ship.

The idea that the younger Princess Shroob usurped the place of her elder sister as the supreme leader of their people and deliberately ignored her existence seems fairly likely from these pieces of evidence. A final relevant aspect is that the younger Princess Shroob is demonstrably aware of how to free her elder sister. After she is defeated is the only time she acknowledges the existence of the elder princess in the game:

“Now it’s your turn, sis...ter!!!”
Young Princess Shroob, Mario & Luigi: Partners in Time

Not long after this, Baby Bowser takes the final piece of the Cobalt Star from Princess Peach and the elder Princess Shroob is revived. The younger Princess Shroob thus knows how her sister can be freed and on top of that, knows it is imminent. As a last-ditch effort to crush the Mario Brothers, she gives her sister a chance to do so. The only time the younger princess acknowledges the elder one, is when she is on the verge of defeat and needs her sister to do the heavy lifting.

The role of the Shroob people


But if the younger Princess Shroob orchestrated a plot to keep her sister sealed, what is the role of the Shroobs as a whole in this? First of all, are they aware of the elder princess’s sealing? A crowd of Shroobs is shown to have been present when it happened in a flashback that happens when speaking to Toadiko. While the elder Princess Shroob is not shown in the flashback, she is seemingly indirectly mentioned by Peach in the Japanese version of the game. She specifically says:

“あなたたちは何者ですかっ!? (DeepL translation: “Who are you people?”)”
Princess Peach, Mario & Luigi: Partners in Time

Of note is the use of “あなたたち”, a second-person pronoun. While she could be addressing the crowd, she only says it after Princess Shroob enters the frame. It might be that the elder princess is lurking just off-screen in this flashback. Either way, the Shroobs would be aware.

They also clearly go along with the plot. Shroobs actively guard one of the pieces within the Vim Factory. Furthermore, on two occasions when the Mario Brothers are about to learn the existence of the elder Princess Shroob, the Shroobs intervene so they don’t. The first is in Toadwood Forest when Toadiko explains what happened after she, Toadbert and Princess Peach first arrived in the past. When she is about to discuss the Cobalt Star, Shroob UFOs appear and turn her into a purple Mushroom. Later, in the Star Shrine, Toadbert reveals on a dirty sketch he gave Mario earlier a drawing of a second Princess Shroob. When he is about to explain what the second Princess Shroob is, the Elder Shrooboid intervenes and similarly turns Toadbert into a purple Mushroom. A third instance of this happens at Shroob Castle when Princess Peach is about to mention the elder princess, but she is interrupted by an attack from the Shroob Mother Ship. This is more likely a coincidence however, given there is no way the Shroobs or Princess Shroob were in earshot of Peach at the time. The first two instances do give the impression that the Shroobs do not want the Mario Brothers to learn about the elder Princess Shroob however. But why is that?

When the elder Princess Shroob is fought at the end of the game, there is a certain pattern in her attacks. In the first phase of the fight, a Shroob UFO may occasionally bring her a drink to heal. Her reaction is to immediately knock the UFO away. In the second phase of the battle, one of her common attacks involves her shooting an energy ball at some UFOs, which make them malfunction and fall on the Mario Brothers. At times, she may combine this with summoning a time hole and sending her subjects forward in time. This gives the impression of a ruler, who despite not being as despotic as her younger sister in her motives, is crueler to her people. She abuses them and is not above using them as weapons against her enemies. The younger Princess Shroob never displays such behavior during the game and in several instances is similarly brought a drink by one of her subjects. In such cases, she does not kick them away and simply stands by. Given this, the Shroobs might cooperate with the plot because the younger princess treats them with more respect than her elder sister and does not abuse them.


The idea is thus clear: in Partners in Time, there is a story about internal Shroob politics happening in the background. Upon the sealing of the elder Princess Shroob, the younger Princess Shroob and the Shroobs as a whole decided to keep her sealed. The younger princess did it because she was power-hungry and the Shroob people did it because the elder princess was a physically abusive ruler. The younger Princess Shroob acts like she is the only ruler of the Shroobs, while the pieces of the Cobalt Star are intentionally kept apart and anyone who speaks of the elder Princess Shroob is silenced. The elder princess Shroob seems none the wiser in the end however, as she describes her sister as follows:

“And my sister… My dear, sweet, beautiful sister… I will avenge her!”
Elder Princess Peach, Mario & Luigi: Partners in Time

The elder princess’s goal throughout the game is focused solely on freeing herself and she does not seem to be aware of the potential plot concocted by her sister and people.