Finally, to unlock the Infinite Ammo unlockable item in Not a Hero you must complete the DLC on the Professional difficulty.
Players who are able to complete the Not a Hero DLC under specific conditions will be rewarded with some extremely powerful unlockable items, which will come in handy when tackling the Professional difficulty.
To unlock the Fast Walk unlockable item in Not a Hero you must find and collect all Antique Coins on Normal difficulty.
In order to collect all the unlockable items in Not a Hero, you will need to complete the DLC a couple of times.