Crysis 2

This achievement will unlock after completing any 6 unique missions on the SuperSoldier difficulty. They don't have to done in order from the beginning of a new game, but you also can't simply select the same mission 6 times.

The easiest way to earn this is if you have already completed the game on an easier difficulty level and have upgraded your suit. With upgraded Stealth, you can pretty much walk through any mission while cloaked as long as you don't get too close to anybody. You only have to find the occasional safe place to duck into cover and let your suit recharge.

Complete (Super Soldier)

1. In at the Deep End
2. Second Chance
3. Sudden Impact
4. Road Rage
5. Lab Rat
6. Gate Keepers

...and the achievement will pop. As aforementioned, you don't have to complete 6 consecutive missions, but if you were doing so from the start, these are the first six (the prologue does count as one level).

This achievement will unlock after completing the level "gate keepers" on supersoldier difficulty. This achievement is stackable with "city never sleeps" achievement which is for completing six levels on veteran difficulty.