From the Super Mario Wiki
Bub is a spoiled Bob-omb kid in Paper Mario: The Thousand-Year Door. He is always with his dad Goldbob and his mother Sylvia. Mario first sees him and his parents in Glitzville, then the Excess Express, and lastly at their home in Poshley Heights.
Bub wishes to work on a train when he grows up, possibly as an engineer. His fascination with trains is made obvious when he states that he'd rather have an autograph of the Excess Express's engineer for a birthday present rather than getting a car, a house, or an encyclopedia set (all three being things his parents thought he wanted).
Despite Bub's overly generous parents and posh upbringing, Bub himself does not possess much money. If the player solves Bub's Trouble (posted at the Trouble Center in Rogueport), Bub rewards the player with his "life's savings", three Coins.
In Bub's trouble, he gets into a fight with Sylvia and needs Mario's help to make up. He wants any ingredient listed within the trouble, then Mario needs Zess T. to make the ingredient. When this happens, Bub wraps the ingredient in wrapping paper, attaches a note to it and gives it to Mario. Then he delivers it to Sylvia, and the trouble is solved.
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