A built-in game feature (not exclusive to DUPLEX but highly utilized by those playing it) allows you to unlock all weapons and infinite health at the start of a new game: Combat Arena Set everything to and difficulty to Select three Gorgons and let them kill you repeatedly. When asked to lower the difficulty, select and quit to the main menu.
The Legacy of Kratos: A Deep Dive into God of War III (PS3-DUPLEX) God.Of.War.3.PS3-DUPLEX