Unlock CO Grit

On Mission 4 in campaign mode, choose Max and then you can buy Grit for 50 coins at the Battle Maps shop

Skip Field Training

To skip field training and get to the main part of the game just complete the last mission, Fog of War in Field Training

Deleted saved games

Hold L + Right + Select when turning on the Game Boy Advance

Advance campaign mode

Successfully complete campaign mode. Enter the battle maps screen and buy the "Advance Campaign" item for one coin. Hold Select and select campaign mode to begin and advanced campaign, with a more difficult CPU opponent. Note: This also unlocks Olaf as a CO

Field Training bonuses

Successfully complete field training mode to unlock the "War Room", "Campaign", "Design Maps", "Stats", and "Special Intel" options.

In-game reset

Press Start + Select + B + A during game play