The Shrooboid Brat is an enemy that appears in Mario & Luigi: Partners in Time, and is fought as a boss in the Koopaseum. Its name is a pun on the term "spoiled brat". The Brat has a different body type from the other Shrooboids; it appears as a larger blue Shroob with yellow spots and large lips, and constantly holds a lollipop.
The Mario Bros. and their baby selves make their way through the Koopaseum, and find themselves entering in the middle of the arena during Princess Shroob's speech in the Koopaseum; the Princess and four other Shroobs retaliate, with the Bros. dodging their ray guns and taking out three of them (except for Luigi, who flies offscreen instead). Princess Shroob then calls in the Shrooboid Brat to defend her, and the monster is flown in, seemingly running into Luigi. The Shrooboid Brat then approaches the other Bros. with Luigi clinging to its lollipop and flings him away, with the baby Mario Bros. hauling him back over before they get into position. The Brat then throws its lollipop, starting the battle.
Once the Shrooboid Brat falls, Princess Shroob calls in six other Shroobs to surround the quarter. The Shroobs pull out hammers and slam the ground, creating a hole under the Bros. that sends them plummeting into the Gritzy Caves as the Shroobs and their Princess cackle.
The Shrooboid Brat's attacks rely heavily on the audience shown on the top screen; they choose its target using cards to create lettered panels - red 'M' panels for Mario and Baby Mario, and green 'L' panels for Luigi and Baby Luigi. The Shrooboid Brat beckons to the crowd each turn, and they will respond using one of two methods.
For the first, they can cast 16 votes on who the Brat should target. The Shrooboid Brat takes the lollipop out of its mouth and throws it at the brother that got the most votes, which is dodged by jumping, and then produces another from its mouth. For the second, the crowd holds up one of each panel and carries two to four mushrooms or Fire Flowers towards them; the mushrooms will sometimes be mixed with Poison Mushrooms. The items are tossed off each of the panels in order and fall into the Shrooboid Brat's hand; it then eats each item before spitting something at the Bros. in the reverse order that they were given to him. Each projectile has to be countered with the hammer to avoid damage; Mushrooms are eaten and spat out as Poison Mushrooms that can poison if not countered, Poison Mushrooms are turned into regular Mushrooms that heal on contact instead, and Fire Flowers become fireballs that can light the Bros. on fire.
As the Shrooboid Brat loses HP, the crowd will cast multiple votes for the lollipop throw, with the "winner" of each vote being targeted in the order they were cast. Eventually, the audience switches the color of the panels to throw off pattern recognition for both attacks (using green 'M' panels for Mario and red 'L' panels for Luigi).
- The Shrooboid Brat, unlike Junior Shrooboid and Elder Shrooboid are the only bosses that have the word Shrooboid, but he doesn't have the same body like them.
- The Shrooboid Brat resembles the Chuboomba, who has a big lollipop.