At the Password Screen, enter the following codes:
Get infinite items, play as a monster, and choose your starting level:

Left, Up, X, Square, Down, Triangle, Square, Down

02 -- Triangle, Circle, Circle, Triangle, Triangle, Up, X, Up
03 -- Triangle, X, Circle, Up, Triangle, Triangle, Square, Left
04 -- Triangle, Square, Circle, Up, Triangle, Circle, Up, Left
05 -- Triangle, Up, Circle, Up, Triangle, X, Down, Left
06 -- Triangle, Down, Circle, X, Triangle, X, Left, Down
07 -- Triangle, Left, Circle, Left, Triangle, Down, Triangle, Triangle
08 -- Triangle, Right, Circle, Up, Triangle, Down, Circle, Left
09 -- Circle, Triangle, Circle, Triangle, Circle, Up, Square, Down
10 -- Circle, Circle, Circle, X, Circle, Left, Up, Left
11 -- Circle, X, Circle, Up, Circle, Circle, Down, Triangle
12 -- Circle, Square, Triangle, Up,Circle, Down, Left, Square
13 -- Circle, Up, Triangle, X, Circle, Down, Triangle, X
14 -- Circle, Down, Triangle, Up, Circle, Triangle, Circle, Square
15 -- Circle, Left, Triangle, Down, Triangle, Circle, Square, Up
16 -- Circle, Right, Triangle, Square, Triangle, Circle, Up, Square
17 -- X, Triangle, Triangle, Square, Triangle, X, Down, Square
18 -- X, Circle, Triangle, Square, Triangle, Square, Left, Square
19 -- X, X, Triangle, Down, Triangle, Down, Triangle, Up
20 -- X, Square, Triangle, Square, Triangle, Down, Circle, Square

Snake Boss:
When you enter the room with the fire breathing snake you will see five columns around the snake pool. Slash those colums with your sword or staff and knock them onto the snake. For best results, use L1 or R1 to move to the next column, then hack away. If you're quick enough the snake won't get a chance to breathe fire.

After all of the columns fall, the fire will stop and the snake will start biting at you. Dodge him when he strikes by pressing L1 or R1. When he starts to swing around the pool strike him in the head. Do this four or five times and he's dead!

Baby Monsters:
To shrink all monsters into babies with baby-like noises, enter the CHEAT MODE code then, while still on the title screen, press L2, L2, R1, R1, L1, R2, Select. You will now see a new option titled "Reduce" when you start the game.

Blurry Screen:
To blur the screen, enter the CHEAT MODE code, then press L1, L2, L2, L1, L2, L2, L1, Select.

Change the Music:
Enter the CHEAT MODE code, then press L1, L1, L1, L1, R1, R1, R1, Select. While playing, pause the game, go to the OPTIONS screen and you'll see a new option called "Current Track." Highlight it and press LEFT or RIGHT to change the music.

Debug Mode:
For debug mode, enter the CHEAT MODE code, then press L1, L1, L1, R1, R1, R1, L2, L2, L2, R2, R2, R2, Select.

Disable Combos:
To disable all combos, enter the CHEAT MODE code, then press L1, R1, L2, L1, R2, Select.

One-Hit Kills:
To cut any enemy in half with one hit, enter the CHEAT MODE code, then press L1, R1, L2, R2, Select