Unlockables

There are several unlockables in the game Tales of Symphonia: Dawn of the New World.

Gladsheim - Defeat the game once, appears in the last chapter of your second or more play-throughs.
Longer Kratos scene -Defeat the game once, can be viewed near the end of the game.
Mania Mode - Complete the game once on any difficulty.
Unknown Difficulty - Complete one playthrough with every battle on Mania mode.
Twilight Palace - Finish all of the "Treasure Hunting" missions that are assigned by the Katz. This will unlock in Chapter 7.

Endings

There are three possible endings that can be unlocked:

Bad Ending - Defeat Marta and Lloyd in the final battle.
True Ending - Prevent Lloyd from stealing any cores other than Lumen's.
Normal Ending - Have Lloyd steal at least 1 core except Lumen's or make bad decisions throughout the game.