Teenage Mutant Ninja Turtles 3: The Manhattan Project Cheats
Press Up(2), Down(2), Left, Right, Left, Right, A, B, Start at the title screen before the demonstration starts. Note: For two player mode press Up(2), Down(2), Left, Right, Left, Right, A, B, Select, Start. Level select, extra lives, and sound test options will now be available.
Auto turtle selection
Press Down(5) at the character selection screen, or Down(10) at the same screen for two player mode. After a turtle is defeated, the next turtle will automatically be selected randomly. Alternately, rapidly tap Left, Right repeatedly at the character selection screen.
When you begin a game, go to the turtle select screen and do not select any turtle. Instead, move your thumb rapidly along the directional pad. Do this until "Auto Mode" appears in the upper right hand corner of the screen, select a turtle and then play. Now, you can be a different turtle every time you lose a life.
To get to the secret option mode, just go to the title screen and press UP, UP, DOWN, DOWN, LEFT, RIGHT, LEFT, RIGHT, A, B and START. Now, press SELECT to get the desired number of players. If you want to play a one player game, press SELECT three times to make the icon back to the one player slot. Once you have done this method, press START and choose your turtle. After that, you will enter the option mode where you will be able to change your number of turtles, select stages, set the difficulty and listen to the sound test.