Unlockable: New Game+
Complete the game and you'll unlock the option New Game+. This option lets you begin the game as Kharg with the following items in his possession: King Statuette, 3 Diamond coatings, 999 Spririt Stones, 10 Bountiful Fruit, 50 Dilzweld Bombs, and 100,000 Gold.
Unlockable: Diekbeck
Beat the 20-round arena trial in Cathena with Kharg's party.
Unlockable: Choco
Beat the 30-round arena trial in Rueloon with Darc's party.
Unlockable: Japanese Dialogue
Hold R1 + R2 + R3 when selection the language. An option for Japanese will appear.
Hint: Answers to Test Questions
After you go to Milmarna and receive knowledge of the Secret Lambda Sutra, go back to Peisus, to the Great Library. Enter the secret room where you've found the Lambda sutra. Now you will meet (yellow) 'Dieckpeck'. Choose not to believe him, and he will test your game knowledge. Here are the answers to the 10 questions:

#1 - b. Counterclockwise
#2 - b. A cat.
#3 - c. Beautiful stones.
#4 - a. Palkia.
#5 - c. How much to spend on entrants's lunches.
#6 - a. A pair of dice.
#7 - c. The Shinobi Gang.
#8 - d. Lakelta Deimos.
#9 - c. A pipe.
#10 - c. Buster.

Your reward depends on how many questions you have answered correctly (you cannot get all the items):
0-4 correct answers - Diek Screw
5-9 correct answers - Neutrino Charge and Clivis's Book
10 correct answers - Spirit Amulet
Submitted by bwong
Hint - Mount Lambda Test
Having trouble with the Lamda monks where you gotta beat them to cross Mt. Lamda? Yeah, I did too. You shouldn't have trouble with the whole group, but when Maru comes in it's gonna be rough riding.

What I did was I trained him by heading to Nien Forest and surrounding him with everyone ordering them not to attack except Maru. If someone gets low on health, use Tatjana's Medical Machine. Maru should be at least level 30 within 15 minutes! Oh, and don't go doing the Lamda thing without getting Maru's SP Level to the max.
Submitted by nick_wood