Shroobs are little, purple mushrooms. They eat themselves and basically anything because they're always hungry. They appear in Mario & Luigi: Fart On Time., where they try to search for Mario. Princess Shroob (the fat, ugly, stupid one) is their leader. They were all killed by the Toclafane, a race of beans from the future.
Coming to the Mushroom Kingdom
One fine summer day, the Shroobs arrived in the Mushroom Kingdom in hopes of conquering it. On their way there, they spotted a flying, blue box, which happened to be the time-travelling spaceship of Doctor Who. Thinking quickly, the Shroobs shot it down, not knowing that it would cause their downfall. Afterward, they finally landed in the Mushroom Kingdom in order to search for the hero whose name was feared across the galaxy: Mario. They never did manage to find him, as they were driven to extinction by the Toclafane.
After the Shroobs shot down the blue box, it began to malfunction. It opened a portal into the distant future, summoning an army of beans known as the Toclafane. Chief among them was Sir Popplafane, the Shadow Thief, who later became known as Popple. Popple and the Toclafane drove the Shroob army to extinction, but were later killed themselves by Wario's massive fart. Only Popple managed to survive, forgetting about the Shroobs entirely and moving on with his life.