Go to option screen on any level and c-up c-right a d-left and then z this will grant you on easy 1-5, that's because it only goes up to that many on easy on normalit will give you all the levels. Also it will give you a list of codes for cheats such as these. Invincibility, infinte lives, unlimited secondary weapond and a list of what secondary weapon you would like. It will also give you a list of "bosses" such as the Dracula's.
Hard Difficulty
Finish the game with Reinhardt or Carrie. Save your game and select a new, previously unaccessible HARD difficulty mode.
Keep Alucard's Equipment
Begin a game with the "Start with 99 luck" code. After reaching the room with the three Wargs (before the room with Death), kill them all. Then, unequip everything except the Alucard Sword, the Necklace of J, and the Twilight Cloak. This should result in a DEF rating of 12. Turn around, exit left, and return to this room. Kill the first Warg, then jump over the second. If your character gets hit, use either a Pot Roast or a Turkey to heal to survive the next part. After jumping over the second Warg, stand and allow let it lunge at your chracter. It should send your character flying out of the room and past Death. You will be unable to enter the menu screen until the game is saved. Note: The room with Death is entered again, he will steal your equipment anyway, unless you undertake the optional battle with Gaibon and Slogra.
Master code
In the options menu type c-up, c-right, a, d-left, Z. This will give you things like: unlimited lives, ammo, and all sorts of other stuff.
More Gold/ More Red Jewels
While in the tomb chambers on Level 1, stand next to a coffin as either Reinhart or Carrie and press C-left. ( Or whatever button the secondary attack is placed.) The coffin's top usually breaks. Only works if you are next to the coffin not on top of it. The coffin on the top gives you Gold and the bottom coffin gives you Red Jewels.