Letter from Chest
From the Super Mario Wiki
The Letter from Chest is an item from Paper Mario: Color Splash. The letter can be found in a Treasure Chest on Fortune Island. It was placed in the chest by Snifit or Whiffit after the game show had taken the Instant Camera from the chest to use as the prize for their bonus round. When Mario collects the Letter from Chest, Huey mentions that they should probably collect the prize before continuing, hinting at its importance in the battle against Wendy O. Koopa. The Letter from Chest has no use in gameplay, and it stays in Mario's inventory for the rest of the game.