Open all Levels
Enter the following code at the main menu: X, TRIANGLE, CIRCLE, LEFT, UP, RIGHT, L2, R2

Weapons
Each weapon is unlocked by completing the mission and achieving the Silent Assassin rating.
Mission 1: CZ 2000 Dual Pistols
Mission 2: Micro Uzi Dual Submachine Guns
Mission 3: Silverballer Silenced Dual Pistols
Mission 4: Magnum 500 Dual Pistols
Mission 5: Sawed-Off Shotgun Dual
Mission 6: M4 Carbine Silenced Assault Rifle
Mission 7: SG220 .S Dual Pistols
Mission 8: MP5 Silenced Submachine Gun
Mission 9: AK 74 Silenced Assault Rifle
Mission 10: GK 17 Dual Pistols
Mission 11: Micro Uzi Silenced Dual Submachine Guns
Mission 12: PGM Silenced Sniper Rifle

Come back to Life
When your health bar reaches zero the game will enter a black and white death sequence. If you are able to get four consecutive head shots on four different enemies during this sequence you will receive a small amount of health and return to the game.

Mini Gun
The mini gun is held by a patient who is behind the locked doors of a basement room in Mission 1: Asylum Aftermath. The keycard that unlocks the doors can be found during Mission 9: The Wang Fou Incident. It is called Orthmeyers Keycard and is on Lee Hongs desk in his office on the second floor of his mansion. After finding the card, finish the mission and save your progress. Quit to the main menu and replay the first mission. Head to the northern section of the map and turn right in the small room with the red flashing sensor on the ceiling. Pass through the west door and dispose of the patient in order to collect the mini gun