McGoomba is a Goomba who is a fugitive who hides behind Zess T.'s kitchen in the town of Rogueport in Paper Mario: The Thousand-Year Door. When spoken to, he states that he's "a wanted Goomba" and has stolen from even Bowser himself.
During the events of the game, 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.