Enter the following at the password screen

Password - Effect :

S D S D R L D - Abyss
L R S R D R D - Fatal Blow
R L M R D S L - Lose Shuriken
S L S D R D L - Nightmare
M R L M R M R - Pizza Paradise
D R S L L S R - Poison
D R M S R L R - Self Recovery
M L D S R D M - Squeaking
L D R M R L M - Super Defense Power
R D S R M R L - Super-Tough
S S S M R D D - Toddling
D S L R D R M - New Nexus outfit for Donatello
L M R M D R D - New Nexus outfit for Leonardo
M L M R D R M - New Nexus outfit for Michelangelo
R M S R M D R - New Nexus outfit for Raphael
M R M D R M D - Challenge Code Endurance - stamina restore no longer available
D S R D M R M - Cheat Code Health