Sound Test
On the Title screen, simultaneously press and hold Down, Select and A for about five seconds.

Stronger Punches
Buy two packs of punches and use the first pack until there is only one punch left, then begin to use the other pack, you wil notice they are much stronger !

Retirement
When you are in the beginning of the game and you lose a person on your team there is a cheaper and easier way to bring them back to life instead of going to the house of life. Simply go to the guild and retire that character. You can pick the same person or a different one. The equipment the dead team member had will go to the new person if it is the same type. If you are in the middle or towards the end of the game I recommend against doing this unless they are all out of hearts and you can't afford to buy any more hearts. If you do it in the middle of the game the new character will not have the upgrades you gave to the old one.