If you're aware of the debug mode code in the original or any other version, it's basically the same here. If not, activate the level select. To do this, go to sound test, listen to sounds 19, 65, 09 and 17 in order. Go back to the title screen, press A and Start, then, in the level select, listen to sounds 1, 9, 9, 2, 1, 1, 2 then 4 in order. Pick a stage while holding A and Start.