Go to the "Royal Chapel", equip the Spike Buster armor and run through the hallway of spikes. After the hallway, Maria will give you a Green Ring.

Use the Green Ring in the center of the Castle at the Clock Tower.

You will quickly be given a second quest.

Cool tunes:
Put the Castlevania: Symphony of the Night CD into an audio CD player. Go to the second track to hear a hidden song.

Axe Lord Armor:
After beating the game once, start a new game and enter your name as AXEARMOR. You'll find a cool new suit of armor in your inventory.

Alucard's Special Moves:

Hellfire (15MP): up, down, down-right, right and square.

Summon Spirit (5MP): left, right, up, down and square.

Soul Steal (50MP): left, right, down-right, down, down-left, left, right and square.

Dark Metamorphosis (10MP): left, up-left, up, up-right, right and square.

Tetra Spirits (20MP): hold up for 2 seconds, then press up-right, right, down-right, down and square.

Wolf Charge (10MP, must have "skill of wolf", and must also be in Wolf form): down, down-right, right and square.

Sword Brothers (30MP, must be using the "Sword" familiar for this to work): down, down-right, right, up-right, hold up for 2 seconds, then press down and square.

Wing Smash (8MP, must be in bat form when performing this): hold X, up, up-left, left, down-left, down, down-right, right and then release X.

Belmont's Special Moves

Whip Uppercut: down, up and X

Run: right right, or left left (hold after second press)

Whip Twirl: hold Square, then tap any direction repeatedly

Slide: down and X

Slide Jump: down and X, X again immediatly after the first one

Back Flip: X twice, quickly

Whip Dash: up, down, downright, right and square (Richter is invulnerable when performing this)

Whip Lunge: left, then right and square(or vice versa)

Enhanced Luck:
After beating the game once, start a new game and enter your name as X-X!V"Q. You'll start with 99 luck and the Lapis Lazuli item, but your strength and hitpoints will be reduced.

Extra Options:
At the name select screen, enter your name as AXELORD then go to the Settings screen

Play as Richter - Japanese and American
After beating the game once, start a new game and enter your name as RICHTER. You can play now as Richter Belmont.

Easy Familiar Experience:
Ok, easy way, but a bit time consuming, to get experience for all your familiars. I believe you have to have it beaten once first. but I may be wrong.

As you start the game, go through like you normally would. But this time, don't but alot from the librarian. Only get the Jewel of Open, and 1 or 2 Library Cards. The proceed with the game.

Once you get in the inverted castle, keep going and get AS MUCH MONEY AS POSSIBLE. Once you get 500,000 go back to the librarian, and purchase the Duplicator. Then go BACK to the inverted castle, and equip it. By this time, you should have at least ONE of the Power of Sire items. Equip that as well. Voila, you have an infinite supply now as long as you have the duplicator equipped.

Now go to the room in the inverted church thing (forgot the name off hand), and enter the room with the big sword that is surrounded by spears and shields. Use the Power of Sire, then leave the room, and go back in, use it again, and so on and so forth. Within an hour I had ALL my familiars powered up to 99/99

Effortless Experience Gain:
To get effortless experience follow these simple steps:
Play through the game like normal until you get your bat familar. at this point go back to near the start of the game where the zombies keep coming out of the ground. Then all you do is stand on the step on the stairs where the zombies can't reach you and turn your bat familiar on. Just make sure that you are far enough away that the zombies won't hurt you if your familar misses one of them.

The bat familar will kill most of the zombies that appear, also make sure you are looking in the direction of the zombies or the bat will not hit them. The best part about this trick is that the familar will kill the zombies and both he and you will get the experience making this absolutely simple in gaining levels. In three hours my bat went from level 2 to level 60!

Find Sword of Dawn and Great Sword:
The Sword of Dawn is hidden in the Reverce Castle. Remember where you got the double jump relic in the normal castle? Well, to the left of that there's a secret breakable wall. Attack it to reveal a hidden pot roast. But when you're in the Reverce Keep, repeat the process to reveal the Sword of Dawn. Execute this move to summon Dawn warriors: down,forward,then square or Circle. Meanwhile the Great Sword can be easily obtained by defeating a gold Armor Lord in the Reverce Castle. It won't always work though. Keep trying.

How to get the Crissaegrim:
First, you must go to the inverted castle. From there, go to the Forbidden Library. There you will encounter some enemies called Schomoo. Those things sometimes drop Ramen and they rarely drop the most powerful sword in the game, the Crissaedrim.

Special Sword Attack:
In order to this you must equip any of these three swords: the Alucard Sword, Jade Katana and Katana Blade. Just press down, front twice and then press circle or square. Alucard will have a mirage that will attack at the back of the enemy, Alucard is also invulnerable in doing this attack.

Summon the Skeleton Warriors:
In order to Summon the skeleton warriors you must equip the Sword of Dawn, then press down, front twice and then press square or circle. A flash of light will release in the sword and there emerge many types of skeleton warriors, such as mages, spearmen, swordsmen and archers.They will help you in battle for a short time ,but you can summon them anytime you want.

Axe armor and other items:
To do this cheat you must have the gravity boots.In the right-side-up castle there is a room under the librarian's room. In this room there is a hole in the ceiling. If you gravity jump up it you push the librarians chair up.You have to keep gravity jumping under him, but you must give time between jumps. (I suggest you gravity jump after you fall back under the ceiling, before you hit the ground.) Keep doing this, though it may take a long while, you will get the axelord armor as well as dracula's tunic, and other items too.

Note: You cannot hit the ground when gravity jumping continuously.