From the Super Mario Wiki
An Intern Shroob is a smaller, light-colored Shroob that rides on the back a Shroobsworth in Mario & Luigi: Partners in Time. Intern Shroobs ride piggyback style, similar to how the Baby Mario Bros. hold on to their older counterparts. Intern Shroobs are found Shroob Castle, with Shroobsworths.
In a battle, an Intern Shroob aids a Shroobsworth by firing energy blasts from a cannon and by tossing dark meteors. However, once the Shroobsworth is defeated, the Intern Shroob knocks the Shroobsworth out and continue the fight in place (just as when an adult Mario brother falls, his younger self takes his place). The Intern Shroob does not directly fight its opponents. After the Shroobsworth gets defeated, the Intern Shroob will spend an entire turn doing nothing; instead, it uses a bio-engineered 1-Up Mushroom to revive the Shroobsworth. Once revived, the Intern Shroob gets back on the Shroobsworth's back and continues the battle as a team.
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