From the Super Mario Wiki
“Listen, this is a huge secret, but I don't mind telling you... I'm a wanted Goomba.”
McGoomba is a Goomba fugitive who hides behind Zess T.'s house in the town of Rogueport. When talked to, McGoomba states that he's "a wanted Goomba" due to a crime he committed in another place, which is why he's hiding in Rogueport. Throughout the course of the game, McGoomba makes escalating boasts about how wanted he is and the severity of his crime, even claiming he stole from Bowser himself. However, if Mario talks to McGoomba before the final chapter, he nervously asks Mario if he ever stole from his mother, implying this is the true reason he's hiding in Rogueport.
During the events of Paper Mario: The Thousand-Year Door, the self-acknowledged criminal pays Mario to deliver a mysterious package to Goomfrey in his trouble. It is unknown what is inside this package (which is simply labeled "Box" in inventories), although it is apparently something very dark and secret as McGoomba wants Mario to deliver it quickly and not let anyone see him or it, refusing to even tell Mario what's within it. After Mario successfully delivers the Box to Goomfrey, even that Goomba is surprised, telling Mario to forget that any of this happened and to tell McGoomba he will somehow dispose of the Box's contents in a way that nobody will ever see them. Mario can later return to McGoomba for a reward of twenty Coins for "saving his neck", although it was never revealed what was inside the Box.
A Star Piece can be found hidden under a ground panel near McGoomba, as well as another on the back side of the roof of a house he hangs around.
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