Ninja Gaiden Sigma Codes -

Cheat Mode
On the mission mode screen press the following buttons to unlock 5 extra missions (available in the Collector's Edition):

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Unlock Mission Mode
To unlock mission mode, beat the normal difficulty setting in story mode.

Difficulties
When you beat the game on any difficulty, you unlock a higher difficulty:

Hard - Beat the game on Normal
Master Ninja - Beat the game on Very Hard
Ninja Dog - Die 3 times
Very Hard - Beat the game on Hard

Golden Scarab Rewards
By collecting a certain amount of hidden Golden Scarabs, Muramasa (shop owner) will reward you with items and weapons that will help you in the game. There is a total of 50 Golden Scarabs in the game. Note: There are NO Golden Scarabs when playing as Rachel.

Armlet of Fortune - Collect 40 Golden Scarabs
Armlet of Potency - Collect 5 Golden Scarabs
Dabilahro - Collect 20 Golden Scarabs
Great Spirit Elixir - Collect 35 Golden Scarabs
Jewel of the Demon Seal - Collect 45 Golden Scarabs
Life of Gods - Collect 1 Golden Scarab
Lives of the Thousand Gods - Collect 10 Golden Scarabs
Plasma Saber MkII - Collect 50 Golden Scarabs
Spirit of the Devils - Collect 15 Golden Scarabs
The Armlet of Benediction - Collect 30 Golden Scarabs
The Armlet of Celerity - Collect 25 Golden Scarabs