Successfully complete the game to unlock the crazy difficulty setting and Trevor Belmont as a playable character. Start a new game with @CRAZY as a name to enable crazy mode. Start a new game with @TREVOR as a name to play as Trevor. Note: Trevor cannot craft items or use innocent devils.
Successfully complete the game then enter a warp room to access Boss Rush mode.
Unlock Moebius Brooch:
Successfully complete the game under the crazy difficulty setting to unlock the Moebius Brooch for purchase at the shop.
Sound Mode option:
Successfully complete Boss Rush mode to unlock a the music box in the warp room. Use it to get the Sound Mode option to hear the game's music.
Easter Island statue:
Have a saved game file from Castlevania: Lament Of Innocence on your memory card to get an Moai statue worth 5,000 gold.