All Ninja items
At the item selection screen, press Square(3), Circle, Square, Circle(2), Left, Up, Down, Right, R2(2).
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More inventory space
At the item selection screen, hold R1 + Square and press Right, Down, Left, Up.
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Full map
While playing a game, hold Select to display the map, then press Circle(5)
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All missions in mission editor
Enter the custom mission screen in the mission editor, then hold R2 + Circle and press Up, Down(2), Right, Left(2).
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Game levels in mission editor
Enter the mission settings screen in the mission editor, then hold Circle and press Up(2), Down(2), Left, Right.
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Office tileset in mission editor
Enter the edit mission screen in the mission editor, then highlight the "New Mission" selection. Hold L2 and press Circle, Square, Left, Right, Circle, Square. If you entered the code correctly, you will hear a sound.
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More options in mission editor
Simply advance in the game to get more options in the mission editor. As your character reaches new levels with new tilesets, the same tileset will then be available in the editor.
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Play as Tatsumaru
Successfully complete the game with both Rikimaru and Ayame.
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Hints
High jump
If you are in certain levels (Quarantine Village, Laborers), you do not need a grappling hook to get on to the roof of a house. Run up to the wall, face it, and jump. Your character will jump twice the normal height of the usual jump and land on top of the roof without hanging on the side.
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Easy kills
Hit an enemy who is not aware of your presence in the head with a blow gun dart to automatically kill them.
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Automatic stealth kill
You do not need to pull out your weapons to perform a stealth kill. Run to the enemy and press Attack. Your weapons will instantaneously be drawn out, and you will perform the stealth kill.
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Stealth kills
You can get the different stealth kills by being in the correct position in relation to the enemy.
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Easy stealth kills
Sneak up from behind.
Sneak up from behind and crouch.
Jump on enemy, while pressing Attack in mid-air.
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Moderate stealth kills
Sneak from the side.
Hard stealth kills
Sneak from front (or wait for them to turn around into you). Note: This must be timed perfectly.