Use the following hint to get a combined clear time for the entire game of under five hours (which is necessary to unlock unlimited RPG ammunition). Play under the Amateur difficulty setting and just run passed all enemies. Only kill story-driven enemies (ones that hold key cards or those that must be defeated to advance the game) while avoiding any crates, barrels, or treasures. Try this with a friend instead of the CPU to get by faster. Note: You do not need to purchase the infinite ammo in "Bonus Features" as you would do for normal guns.