I recommend getting the Magnum as it makes this mode a cake walk, other than that Adrenaline is a must unless you are extremely skilledThe mechanics to this mode are very simple, you have to survive until 5:00 AM fending off waves of Molded. Each hour that passes will get increasingly harder. You can purchase upgrades and ammo through collecting Scrap from the heap collectors. There are 4 in total. 1 in the spawn room, 1 in the scorpion key room, one in the workshop(Behind Corrosive) and one in the morgue(Behind Corrosive). In the playthrough that I completed, I only used the 2 collectors that were available from the start. At the end of every round you will get a warning to either kill all enemies, or kill Jack. Once this notification pops up, all scrap collectors will stop producing scrap in 40 seconds. Kill all the enemies or Jack to proceed on with the next round. Scrap collectors will restart every round without intervention. Scrap collectors will only collect to 1000 Scrap before filling up. Also, I recommend upgrading the handgun first as when it's fully upgraded you can 2 shot standard molded enemies.
Here is what I recommend you starting out with
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Note: This "method" needs you to unlock Adrenaline and extra starting scrap. While they are not necessary, they help out a lot-Knife
-G17 Handgun
-Shotgun
-3 Sets of Handgun Ammo
-2 Health Upgrades
-1 Healing Upgrade
-AdrenalineSo starting out the first round will be standard enemy’s. You have your normal walker molded and then you have those super annoying ankle biters that jump around everywhere. Other then that, this is a relatively easy round. Make sure to activate the scrap machine in the room where you get the Scorpion key in the main story. Kill all the enemies to proceed.
Now at the end of each round you will get bonus points depending on how you did. Killing enemies with certain weapons yields more scrap. Use this bonus scrap you earn to purchase any big upgrades that you need.
Moving onto the second round, it’s pretty much the same until you reach the very end. This is where you encounter the first Jack boss Fight. He uses his shovel as his main weapon here. He is a bit of a bullet sponge, but eventually he will go down. I’d recommend using the Shotgun and Handgun for this fight.
The third round is just the same, only difference is you have a Fatty Molded at the end of the round. Just take him down using whatever you please, I’d recommend picking up the grenade Launcher to take him down. The magnum can also down him in 2-3 shots if you have it unlocked.
The only difference between the third round and the fourth round is that you will now have two fatty molded at the end of the round instead of just one. Make sure you have plenty of ammo for this and once again, the magnum can down both of these molded in one clip.
The fifth and final round is similar to the second round. At the end of this round you will fight Jack for the final time. This time he has his chainsaw scissor monstrosity. Be aware as this can one hit you, I believe blocking doesn't help at all with a certain attack. This is where the adrenaline will come in handy because if you do die, you will be revived. Jack is a huge bullet sponge, so take a couple of shots then run away and keep doing that until you take him down.
EDIT: Video Walkthrough