Assassination mini-game
     Complete campaign 4.

Cow Bouncing mini-game
     Complete campaign 3.

EMP Cannon Range mini-game
     Complete campaign 2.

Long distance hits
     Use  the  sniper scope to zoom in on an enemy, then you can shoot
them with unguided rockets or the cannon without a lock-on.

Saving missiles
     Shoot fuel barrels when they are next to enemies using your cannon.

Sniper Rifle Range mini-game
     Complete campaign 1.

Thermal scope
     Use  the  thermal  scope  during  the  day  so  you don't confuse
vehicles with soldiers.