Go to the Aqua Ruins til you hit the Geo Gate in the Ocean Cave and use it, then come back.As you enter, go the your right and their should be a big shell thingy and push circle to crack it.You will receive a mana egg, skill book, or an OK item.Keep repeating this if you want alot of skills books(extra book carries 3 C-skills) and mainly aqua eggs but stone and wind eggs too.
Try to kill Lucky Mink, a rabbit-like creature. It only has 18 to 20+ HP, but gives over 40,000 experience for each character when killed. It first appears at Starry Corridor level 11 to 14. The Creature is fast, difficult to kill, and will try to escape most of the time. If you want to face it, you need to carry the skill "Coercion" (three of them), and use Mana Eggs that have many hit abilities, such as Zap All, Diamond Dust, Galactic Bang, etc.
Press and hold L1 L2 R1 R2 then while holding press start and select at the same time
Successfully complete the game and save when prompted. Reload the saved game to access a new dungeon with 100 floors.