Castlevania Chronicles Hints & Cheats

Hold L1 and R1 while selecting Original Mode, and you'll unlock an option to change the music played in the game. This works in Arrange mode, as well.

At the title screen do this (slightly modified for domestic release's button layout) classic Konami code:
Up, Up, Down, Down, Left, Right, Left, Right, Circle, X, Start.
Once done, a screen will come up showing ''Extra Option'' where there's a Date set and a Display Mode set.

Enter your name as NOMIS... and you will start the game with much less energy than usual. This in effect will make the game more challenging.

Successfully complete Arrange Mode to unlock Time Attack Mode where you can try to better your stage clear times.

For every stage you complete in Arranged Mode (there are 26 in all), you will unlock one illustration by Ayami Kojima, the artist for Akumajou Dracula X: Gekka no Yasoukyoku / Castlevania: Symphony of the Night and for Akumajou Dracula X68000 / Castlevania Chronicles.
The illustrations can be accessed by selecting Special Option in the Option menu.

Beat the game at least once. The game will become harder and harder every time you beat it.