To unlock the ACR-2 sniper rifle, start a new game in Single-Player mode and at the difficulty selection menu enter: UP, UP, DOWN, LEFT, RIGHT, RIGHT, DOWN.
In the level where you go into the caves, reach the base that is halfway in water. There will be a waterfall. Go through it. Have a sniper rifle or an assault rifle with a rifle scope equipped. Continue until you see a bar like a jail cell door. Go to your scope on your sniper or gun. You will see little people walking. You can snipe them all and they cannot damage you.
During the caves level of the third mission, there is a hidden pathway behind the waterfall that leads to a sniping position overlooking Al-din's camp.
