Automated Leveling
Go into training mode and create two teams. Place the characters you want to level in one team with full equipment. Place high levels characters on the other team with no equipment. Set both teams to the computer "AI" and let them battle without any input.
Mage Leveling
In training mode, create two computer-controlled teams, each with two characters who specialize in using magic. Make sure that one character on each team is equipped with nothing but healing spells and the other nothing but weak damage spells. The game will run almost indefinitely as the two teams slowly attack each other, gaining experience along the way.
Luck Cards
When you pick up luck cards, you either gain or lose luck. To guarantee that you gain luck each time, simply restart the game every time you lose luck and save every time you gain luck.
Music Mode
Enter "MUSIC_ON" as a name to unlock Music Mode. With this mode, you can play background music from all stages.