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Credit goes to OzQuant from 360haven
"I have completed 159/160 in-game challenges for Black Ops 2. All you need to do is re-play Mission 3: Old Wounds and not die. You can play on Recruit difficulty and you can also take whatever weapon and perks (future weapons like the x-ray gun are allowed!) you want. Just need to finish the Missions without dying and that will complete the last challenge for the achievement. This took me a long time to do, and the challenges are sooooo annoying, it ruined the game for me.

Let me know how it goes. I finished the campaign on Veteran difficulty and went back and did the challenges on Recruit. Not sure if any other achievements will pop.

If you want to do the achievement legit (not sure why you would, since you have this save file!), I can try and give you advice on any challenges that you are stuck on."