For the alternative Ending you need the Hacking Tool that you get from the last Sidequest with the Tolga Brothers (it’s at their last Safezone, on a Barrel), with it you can open the Mystery Boxes.
- First open this Box, inside are Nuclear Codes.
- Next you need to find the Military activation code here from a corpse lying underwater
- and lastly the Military transport Key from a Box near the Behemoth Freak.
- then Take all Items to this Truck and see…
You also get the Team Dying Light Outfit for unlocking this more or less unspectacular Ending.