In the past: The Shroobs have gotten tired of living on their planet and wanted a new home so Princess Shroob set off a full invasion of the Mushroom Kingdom to make it her own. She takes over Peach's Castle, turning it into the Shroob Castle. The castle towers were changed into tall purple mushrooms, along with all the pillars and bushes, and even a statue of herself got built.
In the present, the Professor E. Gadd made a time machine. The machine was first used by Princess Peach who goes to visit the Mushroom Kingdom's distant past. She unfortunately came into the time in which the kingdom was invaded by the Shroobs, so she got captured and imprisoned by Princess Shroob. A green Shroob then comes back to the present with the time machine, and was then unusable since the Cobalt Star has been shattered into 6 pieces. A while later, a tear in the space-time continuum, known as a time hole, opens, leaving a passageway into the past. While searching for Peach, Mario and Luigi locate their younger selves, and agree to locate the crystal shards, which are remnants of the Cobalt Star which had been shattered, since they were told that they needed five Cobalt Star shards to gain access to the Shroob Castle.
When Baby Mario, Baby Luigi, Mario, and Luigi rescue Peach in Gritzy Caves, she had a purple mushroom attached to her face. She is later revealed to be Princess Shroob in disguise who had the intention of taking over the present Mushroom Kingdom as well as the Mushroom Kingdom of the past. It seemed Baby Peach was the only one knowing as she cried at Princess Shroob's presence.
After acquiring five shards, the four Mario Bros. eventually make their way through the shroobified Peach's Castle and hijack a Shroob Battleship and engage the Shroob Princess in a dogfight. After blasting the Shroob Mothership out of the sky the Princess emerges from it. She then enters battle with them.
After she is defeated, Mario, Luigi, and their baby selves free Princess Peach. Mario and Luigi explained her that they were searching for Cobalt Star shards, after which Peach shows the last shard and tells them that she cannot allow them to reassemble the Cobalt star. Before she can explain, Baby Bowser, who was hiding in the Mothership, drops in, putting the last Cobalt Star Shard in the Cobalt Star. Peach then explains that Princess Shroob had a twin sister (who actually looks nothing like her, and is call Princess Shroob Elder so she could not be a twin [unless of course it means she was born a short time before this Princess Shroob]), and that Peach sealed Elder Princes Shroob in the cobalt Star, thereafter shattering it into pieces. Reassembling the cobalt star liberated Elder Princess Shroob from the cobalt star, destroying the cobalt star in the impact. Princess Shroob was thought to be the main villain for quite some time.
Princess Shroob remains inside her mecha for her first phase. After it takes 4 hits, she exits the mecha and fights on foot.
Princess Shroob can attack in the following ways:
- Her mecha "walks" over and shoots lasers at the target, then attempts to crush his head. The former can be dodged via jumps, and the latter via hammers.
- She can fire lasers, which can be jumped or ducked under (no action required) depending on their angle.
During her second phase, Princess Shroob fights on foot.
- She can throw energy balls, which the Mario brothers can deflect back at her with their hammers or jump, depending on the oncoming angle. She always teleports wildly while attacking.
After losing half her HP, Princess Shroob gains a star attack in which she throws a star that needs to be jumped on. It loops back and accelerates if it is dodged entirely, being destroyed if it makes contact. If it is stomped on, it has no effect. However, if it hits from the side, the target may suffer random (usually negative) status effects.
Super Smash Bros. Ultimate
Princess Shroob made a cameo in Super Smash Bros. Ultimate as a neutral primary spirit. Like other spirits, she was captured by Puppet Fighters. To claim the spirit, the player must defeat the puppet fighter of Peach in her red costume taking place in Princess Peach's Castle. In appearance, the Puppet Fighter strongly resembles Princess Shroob with similarities. There are conditions to the battle representing Princess Shroob:
- The enemy is giant when the enemy is at high damage, referencing Elder Shroob's battle upon Princess Shroob's defeat.
- The player and the opponent is fighting in Stamina mode, referencing Mario RPG's battles where the enemy is defeated when losing all HP.
- The enemy has increased attack power when the enemy's at high damage, referencing Princess Shroob's battle.
- HP - 3000 (1700)
- POW - 120 (180)
- DEF - 130
- Speed - 60 (120)
- EXP - 0
- Coins - 0
- Princess Shroob's star attack is similar to the one Dark Fawful uses in Mario & Luigi: Bowser's Inside Story while battling Bowser in the battered Conference Hall in Princess Peach's Castle.
- At multiple points in the game, Princess Shroob drinks from a skull-shaped goblet filled with an unknown liquid. It is possible the drink is made with Vim, as Elder Princess Shroob drinks Vim to restore her health during her boss battle.
- Many of the shards of the Cobalt Star were in Princess Shroob's grasp for the duration of the game, such as the shard held by Swiggler in the Vim factory. Ignorance of this would be implausible, suggesting that the younger princess was reluctant to reassemble the star and restore her elder sister to power.
- If the player's level is high enough, it is possible to defeat Princess Shroob in two turns. One turn allows for the shield to break, the other turn to damage her. If Mario and Luigi's speed is high enough, she will not get a turn to attack.
- Princess Shroob is one of few female main antagonists of a Mario game. Others being Cackletta and the Shadow Queen.
- After Princess Shroob's defeat, in the American version it will show the battle reward (which is 0 EXP and 0 Coins along with no items). In the Japanese and European versions, the battle screen immediately fades out after her death animation.