Find a Pinball Machine. Zoom in and place it so that it’s facing away from you while you are facing down. Look carefully at the designs to see Mario on the bottom part and the Mushroom Kingdom on the top part.
In the clothes shop, sometimes they will sell a Luigi hat, called "Lil Bro's Hat". There is also a hat with an “M” on it called the “Big Bro’s Hat”. Also, sometimes you will find the "Big Bro's Mustache" and the "Big Bro's Shirt", which all are things Mario wears.
In Pierce's (the blue eagle) room, open the refrigerator and a message “What are Luigi's clothes doing in here?" will appear.