Castlevania: Harmony Of Dissonance Codes -

Play as Maxim Kischine:
Enter MAXIM as a name after completing the game at least once. He is faster and jumps higher than Belmont.

No magic:
Enter NO MAGIC as a name after completing the game at least once.

Hard mode:
Enter HARDGAME as a name after completing the game at least once. A voice can be heard at the start of the introduction to confirm correct code entry.

Boss Rush mode:
Successfully complete the game to unlock the Boss Rush option. There are three levels (easy, normal, and hard) that must be unlocked by playing each in succession, starting with easy.

Classic Simon:
Unlock Boss Rush mode, then press Up(2), Down(2), Left, Right, Left, Right, B, A, Select at the Konami logo. Select Boss Rush mode to play as the NES version of Simon.

Sound test mode:
Successfully complete the game with the good ending (where you rescue Maxim and Lydie).

Encyclopedia mode:
Get the Monster Tome relic during game play to unlock the "Encyclopedia" option at the "Secret Info" menu, which details all monsters that you have defeated.

Collectibles mode:
Get any collectible during game play to unlock the "Collectibles" option at the "Secret Info" menu, which lists all the collectible items that you have found.

Hint: Gradius reference:
When you combine the Bolt Spellbook with the Bible secondary weapon, your character will have a double orb shield in front of him. This shield is one of the shields from Konami's classic Gradius series, with similar sound effects when it collides with enemies.