Wario Land 2 Cheat Codes for Gameboy

Flagman D.D. mini-game
Successfully complete the game with a 100% status with all treasure and map pieces. Then a bonus game can be played after the final level.

Boss battles
Successfully complete the game with a 100% status with all treasure and map pieces. Then the levels on the map that have a Boss at the end will have a skull nearby, marked with an arrow. Choose one of these levels. Then at the level name screen, hold Down and press A. The game will proceed directly to the Boss.