Tenchu: Stealth Assassins Cheats (PlayStation)

At the item selection screen, press Left, Left, Down, Down, Square, Square, Triangle,
Circle. Then, the armor icon will automatically be selected. Now begin
  game play as Ayame and select her third costume.

First during game play pause the game then hold 
  L1 and R2 at the same time then press up, triangle, down, x, left, sqare, right, circle
in that order.

After you put in the Debug Menu cheat, use one of the cheats. (ex: add guy, secret weapon)
Then if you pause during the game, you can push select as fast as you
  want while it is paused to make the game move frame by frame. You can control the ninjas
during this.

At the item selection screen HOLD L1, then press LEFT, LEFT, DOWN, DOWN, SQUARE, SQUARE,
TRIANGLE, SQUARE.

At the item selection screen HOLD R1, then press LEFT, LEFT, DOWN, DOWN, SQUARE, SQUARE,
TRIANGLE, CIRCLE.

At the item select screen hold L2 then press LEFT, LEFT, DOWN, DOWN, SQUARE, SQUARE,
TRIANGLE, X.

To hold up to 99 weapons, go to the weapon selection screen, hold L1 and press Up, Up,
Down, Down, left, Right, Left, Right, Square, Triangle.

During any time in the game where you have less than 100 health, press start then press:
left,left,down,down,square,square,triangle,square. If you entered it correctly you will
hear a shout and the game will go out of pause mode.

Here is a code that allows you to select the layout A, B, or C of the level you are going
to play. To activate this code, enter the following sequence at the level select screen:
While holding R1, press left, left, down, down, square, square, triangle, X.

Select a character, then hold R2 and press LEFT, LEFT, DOWN, DOWN, SQUARE, SQUARE,
Triangle, Square at the next screen.

First do the debug mode. Then choose enemy option. Choose any enemy (a level 2 ninja would
be thebest). Then choose Pad-2. Then run away from P2. When you see a question mark (near
your life bar)run back to P2. Now Player 2 can move the enemy you have selected for
him/her. Try level 4 (The checkpoint) at the bridge so you and P2 can fight and knock each
other off.

  Note:If leave Player 2 he/she will dissapper.
  Note:If P2 fall in deep water he/she will drown

At the weapon selection screen, hold R1 or L2 and press Up, Up, Down, Down, Left, Right,
Left, Right, Square, Triangle.

Select a character, then at the next screen (mission select), hold L1 and press Left,
Left, Down, Down, Square, Square, Triangle, Circle. Note: Japanese voice effects
  will start after the first level; the narrative will remain in English.

On the stage select screen (levels appears when you've beet them) hold R2 and press Up,
Up, Down, Down, Left, Right, Left, Right, Square, Triangle.