Search the following background locations to find Luigi in the background. When you have found Mario's brother and peeled him off ALL five locations by Paperizing he will become unlocked in the credits sequence. Each time you peel off Luigi, you can read an amusing newspaper article in the leftmost house in Decalburg's Residential Area.
On the bridge leading to the central tower (search the background).
On the fourth floor of the tower, in a window at the far right end of the second outdoor walkway.
On a rock formation sticking out of the ocean that is only visible from the pier.
Near the end of the chairlift after the enemies stop coming; appears only briefly.
In the background to the left of the hot springs.
Added by: Sanzano Nov 26th 2012, ID#490