Easy experience
There is an enemy who is weak and will give you lots of experience with little effort. He's called Lucky Mink and is on levels 11, 12, 13, and 14 only. Go to the starry corridor to find him.
In-game Reset
Hold L1 + L2 + R1 + R2 and press Start + Select during game play.
Bonus Adventure
Successfully complete the game and save when prompted. Reload the saved game to access a new dungeon with 100 floors.
Extra Bosses
After gaining access to the Starlight Park, return to the various ruins and proceed to the end of each. You will find a Boss or group of Bosses to defeat. It is recommended that you be at level 30 or higher.