Start game as usual, goto to the Password section under Options and 
enter the following codes: 

Effect Password 
Alternate costume for Donatello1  LMSSL 
Alternate costume for Leonardo1 MSRLR 
Alternate costume for Michaelangelo1  MMMSL 
Alternate costume for Raphael1 SMLSR 
Attack power up for Donatello DRLDS  
Attack power up for Leonardo LMLSD  
Attack power up for Raphael RDSRL  
Alternate attack sound effects SLSRS  
Defense doubles for Donatello LRLDD  
Defense doubles for Leonardo SSRSL  
Defense doubles for Michaelangelo LSSDR  
Defense doubles for Raphael DSRRS  
Defense power up for Michaelangelo MSRMM  
Master Splinter in story mode LDRSM  
Playmates toy database LSDRM  
Power up effects double for Donatello SDDLS  
Power up effects double for Leonardo LDDRS  
Power up effects double for Michaelangelo LMLMS  
Power up effects double for Raphael DLDRS or LMMDR  
Unlimited fire shurikens and all food is pizza for Michaelangelo  MDMSL 
Unlimited Shurikens for Leonardo SRRDM  

Letter abbreviations are as follows: 
M - Michelangelo 
D - Donatello 
L - Leonardo 
P - PiZZADOX 
R - Raphael 
M - Master Splinter 


Challenge mode:
Successfully complete story mode as Raphael, Donatello, Michaelangelo, and 
Leonardo. 

Casey Jones:
Successfully complete level 1 as Raphael to unlock Casey Jones in versus mode. 

Evil Turtlebot:
Successfully complete level 3 as Raphael, Donatello, Michaelangelo, or Leonardo 
to unlock the Evil Turtlebot in versus mode. 

Hun:
Successfully complete level 6 as Michaelangelo to unlock Hun in versus mode. 

Oroku Saki:
Defeat Saki as Raphael, Donatello, Michaelangelo, or Leonardo to unlock Oroku 
Saki in versus mode. 

Shredder:
Defeat Shredder as Raphael, Donatello, Michaelangelo, or Leonardo to unlock 
Shredder in versus mode. 

Splinter:
Successfully complete Dojo level 3 as Leonardo to unlock Splinter in versus mode. 

Yoshi Hamato:
Successfully complete Challenge Mode as Raphael, Donatello, Michaelangelo, or 
Leonardo to unlock Yoshi Hamato in versus mode. 

Alternate costumes:
Set the 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. 

Unleash the Secret of Gembu 
Beat the third Dojo Stage with all four turtles to learn the Secret of Gembu 
maneuever. Use the move to damage everyone on the screen. You'll have three 
opportunities per level to use it.