On November 20, 2009, Nintendo revealed passwords for extra missions in Pokemon Mystery Dungeon:Explorers of Sky. Pokemon Mystery Dungeon transforms players into a Pokemon, based on a quiz that players take at the beginning of the game. Players then go through missions, leveling up their Pokemon and their teammates, recruiting more Pokemon for their cause, and exploring dungeons. The official site for the game can be found here.
A full list of missions can be found here, at the official website for the game. The missions the codes unlock are of varying difficulty and reward, but as any good mystery dungeon player knows, take every quest and reward you can get! (Please note that at one point, some of these missions were available for download from the Nintendo Wi-fi.)
Article from Gamersyndrome.com