Make sure you get an overall of 85% on the 1st Campaign.
Bonus Mission 2
Make sure you get an overall of 85% on the 2nd Campaign.
Bonus Mission 3
Make sure you get an overall of 85% on the 3rd Campaign.
Bonus Mission 4
Make sure you get an overall of 90% on the 4th Campaign.
Hidden introduction sequence
Remain idle at the main menu for about five minutes. A hidden sequence will play, revealing much about the game.
Weapon Fiddling
By holding in the A button when you have a motar or bazooka you can increase the range and the fire power of the weapon. Also, if you have assault troopers and your gun is constantly becoming over heated try to keep your gun in the sweet spot,spot that enables you to fire the most rounds, just let go of A and hold it repeat and you can lay down more cover fire then an MG nest.