Ok so if u are like me and u have reupped quite a few times but have used up all your rare boxes for stupid xp, and as a result are still missing the gold skin for the required weapons needed for the "golden artifact" achievement, then your in luck. You can earn epic/rare/normal boxes MUCH faster!
1) Delete your GOW:J player data from your HDD (Make a back up just in case) then disconnect from your internet so u can play offline. If u did it correctly once you start up GOW:J your rank will now be reset to level 1, but dont worry you can revert back once you reconnect back online later.
Do not delete your campaign file!
2) Now that you're level 1 all boxes will be much faster to attain. So what u wanna do now is to play Aftermath Chapter 2 using the 3x Retro charge ribbon boost. You can get about 10 ribbons every 2 mins and all you'll need is 50.
Or you might prefer to use the silverback section.
3) Once u have earned as many epic/rare/normal boxes as u want (I recommend every rare prizebox) finish the section and exit to main menu. Check to see all boxes you have earned, now just go back to your dashboard and reconnect to internet and boot up GOW:J as normal. Once you enter the main menu you should be reverted back to your old rank with everything else such as ribbons/medals intact. But now you will have some boxes that will reward u with skins only due to the TU2 patch. If you still dont have enough boxes for the golden skins just repeat from step 1.
