Maximum levels, gold, and ring power
This trick can be used at any point in the game. Buy the Amulet from the magic item shop. This may seem like a waste of money, but has a special power. If you are about to raise a level, use the last charge (third use) to kill the monster which would of raised your level. There should be a one-second delay followed by a flash of light. If done correctly, your level, gold, and ring power will be maxed out.
Restore health
Hold Up on controller two when the Sega logo is displayed. During game play, enter the status screen. Hold C and press Up, Down.
Adjust power level...