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