Sniper Shot can kill an enemy with just a single shot. Use the red box as an indicator for an incoming enemy plane. Place your crosshairs on the center of the red box accurately before firing. This will require practice, as you have a very limited time. Try this with quick scoping to save time. Tap the scope icon and repeatedly tap the attack icon several times so you can release and fire immediately. Shotgun Shot can kill groups of enemy planes instantly but only at close range.