Castlevania: Harmony of Dissonance Cheats

To unlock Sound Mode, where you can listen to all the music from the game- You must have all Dracula parts and you must wear Juste's and Maxim's ring when fighting Maxim in Castle B. Afterwards, the final boss will show up. Defeat him to get Sound Mode, which you can select at the main menu.

There are 2 options in the Secret Info menu in the game that you can unlock:

Encyclopedia: A list of every monster you've defeated, along with stats on them. Unlock by collecting the Monster Tome relic.

Collectibles: A list of all the collectible items you picked up (used to decorate Juste's Room). Unlock by simply picking up a collectible for the first time.

To unlock the Boss Rush mode, where you play every single boss again, one after another, simply beat the game.