Debug Mode

You must delete your save first before you can do it. Use the last option in the main menu.

While selecting the new game option, hold R + Left C + Right C + Z + A, make sure to hold A last.
A new screen will appear with a bunch of settings. Use C-Up to access TYCONF.SF tab, C-Left to access TYCONF.SU tab, and C-Right to access TYCONF.SU(28) tab.
You can select an option by using the Control Stick, and press Z/R/A/B to change the option's value that's attributed to it.

WARNING: Do not enable TYCONF.SU DEBUG (Option 15) on a flashcart as it may corrupt the SD card, and on an emulator, the game will potentially glitch.