Play as 8-Bit Simon:
After you've beaten the game and obtained Boss Rush Mode, input the Konami Code (up up down down left right left right B A) while the Konami logo is being shown. Enter Boss Rush mode and Simon will be automatically selected.

Play as Maxim in Boss Rush Mode:
To play as Maxim in Boss Rush mode, press and hold the L and R buttons down when in the Boss Rush menu, and hold them down until you enter the difficulty. You can now play as Maxim in Boss Rush.

Play as Maxim:
After you beat the game, enter MAXIM as your name in a new game and you will start the game as him.

Hard Mode:
Just enter HARDGAME as your name, you will hear sound when you success.

No-Magic:
To play the game using no spellbooks, enter ''NO MAGIC'' as your name when you start a new game.

Unlock Boss Rush Mode:
To unlock the Boss Rush mode, where you play every single boss again, one after another, simply beat the game.

Unlock In-Game:
There are 2 options in the Secret Info menu in the game that you can unlock:

Encyclopedia: A list of every monster you've defeated, along with stats on them. Unlock by collecting the Monster Tome relic.

Collectibles: A list of all the collectible items you picked up (used to decorate Juste's Room). Unlock by simply picking up a collectible for the first time.

Unlock Sound Mode:
To unlock Sound Mode, where you can listen to all the music from the game- You must have all Dracula parts and you must wear Juste's and Maxim's ring when fighting Maxim in Castle B. Afterwards, the final boss will show up. Defeat him to get Sound Mode, which you can select at the main menu.

Easter Egg - Pose Bonuses:
Whenever you defeat a boss (Either in the normal game or during Boss Rush) you can go for a Pose Bonus using Juste or Maxim. These bonuses don't actually do anything, they're simply there to see how well you can time a pose.

To get a Pose Bonus, grab the orb that appears after killing a boss while in the last frame of Juste or Maxim's attack (IE, when Juste's whip is fully extended, or Maxim's sword is completely out). If done successfully, you'll see a Pose Bonus message like 'GREAT!' appear over your character.

The higher in the air you are when you do this, the better your Pose Bonus.

All Endings:
Defeat the final boss in Castle B and wear the JB and MK bracelets. You will then fight the true boss and will recive the best ending. Unlocks Boss Rush Mode and Sound Mode. Defeat the final boss in Castle A. You will recive the ok ending. Unlocks Boss Rush Mode. Defeat the final boss in Castle B, but don't wear any of the bracelets. You will recive the bad ending. Unlocks Boss Rush Mode.

The Ice Fist Glitch:
This glitch will let you, with proper timing, get to some ledges that are just out of your reach. First, get the Ice Fist (Ice book + Sacred Fist) magic, and then go to the ledge you want to get on. At the peak of your jump, activate the Ice Fist, and, if timed properly, it should get you on top. This can be used to get Dracula's ring and Logoth's ring early, and after you get the double jump, you can get the platinum tip early too.