Go to the options and then go to the password screen. Next you will see 5 symbols:
Use the following keys when entering the passwords:
L: Leonardo
M: Michaelangelo
D: Donatello
R: Raphael
S: Splinter
Alternate Costumes:
Enter the code then hold L or R when selecting your character
Donatello: SRSMM
Leonardo: RMMLL
Michaelangelo: DLDSM
Raphael: LMSDD
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
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.
Holiday Costumes:
Set your console's system date to December 25 to see the turtles with a Christmas theme. Set the system date to October 31 to see the turtles with a Halloween theme.