Beat the game once to unlock Hard Mode. You start the game over on the same file and a brass heart is added to the save file.

You also start with a Ruby Key. Needed to unlock the door at the right of the lobby that is said to need a "special key". It leads to a room with an arcade game that you can actually play. It's called "Thou Art Dead". Plays much like the old Castlevania games, except the character looks like a Golden Axe character, and the monsters are different.

Hard Mode - Beat the game once
Ruby Key - Beat the game once