Shroobs are a race of fungus-like aliens from the Shroob Planet. On their planet, they searched the skies for a new home, and set their sights on the Mushroom Kingdom. Led by Princess Shroob and Elder Princess Shroob, they attacked the Mushroom Kingdom and conquered it.
Mario and Luigi: Partners in TimeEdit
Elder Princess Shroob, Princess Shroob, and the Shroob army invaded and conquered the Mushroom Kingdom in the past. When Princess Peach From the present went to the past via E. Gadd's Time Machine She found the past Mushroom Kingdom in terror. Princess Peach then trapped Elder Princess Shroob in the Cobalt Star, so Princess Shroob took Peach as prisoner. Mario and Luigi travelled back in time to save Princess Peach. They met up with their baby selves. On Star Hill, Elder Princess Shroob pretended to be a Star Spirit and tricked Mario and Luigi into collecting the Cobalt Star Shards. Baby Luigi is the only one who knew it was Princess Shroob and not a Star Spirit, as he was the only one crying. The Shroobs carried out their plan until Mario and Luigi foiled it
Mario and Luigi: Bowser's Inside StoryEdit
In the Fawful Theater, as an easter egg, right before the battle with Midbus, a Shroob can be seen at the bottom right row. Later in the game, a group of three Shroobs are fought (optionally) in the cold storage room of the Bowser's Castle freezer. Various references to Mario & Luigi: Partners in time are made before and after the battle, such as Mario stating that Luigi was the one to ultimately defeat the Shroobs, and Starlow joking that he did it by ferociously crying, referencing Baby Luigi crying, which showed the Shroobs' weakness.