Mission: Crew Expendable
Difficulty: Recruit
From the beginning of the mission, just take out your pistol and don't shoot any bullets. The AI will take out a good amount of the enemies for you, and there are only a few parts where you will required to push forward and grab a couple of knife kills.
If you die, just reload your last checkpoint. Because you are only using your knife and not using a weapon or reloading it, you will also unlock
Retro Shooter:
The mission only takes about 7:30 using this strategy, and doesn't have many hard sections.