Play as Maxim:

Beat the game once, then start a new game and enter the name MAXIM.

Play Without Magic:

Beat the game once, then start a new game and enter the name NO MAGIC.

Unlock Hard Mode:

Beat the game once, then start a new game and enter the name HARDGAME.

Boss Rush Mode:

Beat the game to unlock Boss Rush. You will be put into a series of rooms containing the bosses from the game. The number of bosses depends on the difficulty you select. Harder difficulties are unlocked by beating the easier modes.

Unlock Simon Belmont:

Unlock Boss Rush Mode and play it once. Reset the machine and during the Konami title screen, press Up, Up, Down, Down, Left, Right, Left, Right, B, A. Then start Boss Rush Mode to play with the original vampire slayer!

Sound Test:

Beat the game with the best ending and you'll unlock the sound test mode that lets you listen to all the game tunes.