Okay here is the deal - there are cheats and hacks in most games. Most games are not like Dying Light in that your progress and success is a major element in how much you enjoy the game and game play. Because of that, using cheats and hacks can fully compromise your game play experience.
It is a lot like with the Pokemon games in that you could choose to avail yourself of hacked Pokemon, but doing so took away the sense of accomplishment that you obtained in playing. Same deal here - if you use the cheats / hacks - the most obvious being to duplicate weapons - you remove a LOT of the challenge.
Whether you choose to do this is your call - but we recommend not.
After you obtain and level Free Running Adept and Free Running Expert to 40 XP per skill, head to the Tower and sleep / wait until night, then (XP is doubled at night) then leave the Tower and head down the stairs.
There is a building with two barrels in front of it to the left - climb the barrels and then the building, and when you are at the top just fall backwards. Rinse and repeat this to build mad Agility XP.
For this cheat you need to buy the skill "Melee Throw" (Prerequisites are Power Level 4 and Stun) in the Power Skill Menu.
With that done, equip your most valuable/powerful melee weapon and throw it.
While the weapon is in the air, open your Inventory and drop it (the thrown weapon)/ That will cause it to be duplicated!
You can rinse and repeat this process as often as you like, selling off the extras to get more money to use with the traders and such.
There is a bug in the game that will cause random Achievements to unlock under specific circumstances.
To cause this to happen start the game while logged into a Gamertag that has already unlocked a large number of Achievements and completed a significant portion of the game, then from the main menu screen select the Change
I discovered this bug/hack due to my use of multiple accounts when working on game guides - I often need to repeat sections of a game in order to document and/or illustrate them and so I have a number of accounts that I use for that purpose. While doing so I triggered this hack/bug no less than five times on three different Gold-endowed Accounts.
To duplicate this start the game logged into a Gamertag that has lots of Achievements already unlocked in the game, and a significant portion of the story completed, and then, from the main menu screen,
This unlocked It's All In the Writing (25g) Find all text collectibles, Now It's Safe (25g) Capture all Safe Zones, Trespassing (25g) Complete all Quarantine Zones, and The While Story (100g) Finish all side quests in the span of 10 seconds.
Note that this has the potential to generate false hacking charges, since it will cause Achievements that should not have been unlocked in that order and time scheme to be unlocked, so we have to hope that the folks at LIVE are aware of this, right?
While this is clearly a cheat - you know the guards at the Tower with that slick Assault Rifle? Well... You can kill him by throwing a gas canister at him without gaining aggro.
Once he dies he drops his gun and ammo - which you can then take. No worry he will re-spawn.
Update: This may have been patched - while it previously worked, we were unable to get it to work today (19 March 2015) - but we are leaving it here just in case we suck at it?