Playmates Art:
Go to the options and then go to the password screen. Next you will see 5 symbols (letters. Type in L S D R M that means Leo Splinter Don Raf and Mike. Ok then you should get a message that says PLAYMATES DATABASE IS UNLOCKED. Then go back to the main screen and go to data base. When you click on it a new screen should come up and say playmates with the picture of the turtles click on it and you will be looking at some cool art. 

Michelangelo will get an improved weapon in the story mode:
Go to the options and then go to the password screen. Next you will see 5 symbols Put in MSRMM

Get Challenge Mode Unlocked:
Beat story mode using all 4 turtles

Get Stage Select Levels:
Beat a level to unlock it for Stage Select

Get the Secret of Gembu:
Beat Dojo Stage #3 using all 4 turtles and you get the Secret of Gembu move which will damage all enemies on screen

Get Characters for Vs. Mode Casey Jones: Beat Stage 1 with Raphael
Evil Turtlebot: Beat Stage 3 with any turtle
Hun: Beat Stage 6 with Michaelangelo
Splinter: Beat Dojo Stage 3 with Leonardo
Shredder: Beat Shredder with any turtle
Oroku Saki: Beat Saki with any turtle
Yoshi Hamato: Beat Challenge Mode with any turtle

New Costumes:
Change your PS2 System date to Dec 24th or 25th to get Santa outfits or October 31st for Halloween outfits.

Password notes:
Use the following key when entering the passwords. 

L: Leonardo
M: Michaelangelo
D: Donatello
R: Raphael
S: Splinter 

Alternate Costumes:
Enter the code then hold L1 or R1 when selecting your character: 

Donatello: SRSMM
Leonardo: LDMSR
Michaelangelo: RRLMD
Raphael: DMDML 

Longer bandanna and double attack power:
Donatello: SMLLR
Leonardo: SLDDS
Michaelangelo: SMRDL
Raphael: SRRLR 

Shorter bandanna and double defense power:
Donatello: LLSMR
Leonardo: MLLSR
Michaelangelo: MRLLD
Raphael: LSMDR 

Weapon power-up:
Donatello: DRLDS
Leonardo: LMLSD
Michaelangelo: MSRMM
Raphael: RDSRL 

Infinite shurikens:
Leonardo: MSSRD
Michaelangelo: MRRSL 

Master Spinter in Story mode: LLMSR
Casey Jones in Story mode: SRLMD
Alternate hit sound effects: LSLSS
Playmates toy database: LSDRM 


Hints
Challenge mode:
Successfully complete story mode with all of the turtles. 

Casey Jones:
Complete level 1 as Raphael to unlock Casey Jones in Versus mode. 

Evil Turtlebot:
Complete level 3 with any turtle to unlock Evil Turtlebot in Versus mode. 

Hun:
Complete level 6 as Michaelangelo to unlock Hun in Versus mode. 

Oroku Saki:
Defeat Saki with any turtle to unlock Oroku Saki in Versus mode. 

Shredder:
Defeat Shredder with any turtle to unlock Shredder in Versus mode. 

Master Splinter:
Complete Dojo level 3 as Leonardo to unlock Splinter in Versus mode. 

Yoshi Hamato:
Complete Challenge Mode with any turtle to unlock Yoshi Hamato in versus mode.