After you finish the game , before you start infinity, go back and do training levels again and again. Keep doing this because you will keep getting weapon uprades, you can get each weapon up to version 6. It takes a while but as it's random it does'nt matter it's still fun.( and you can do as many times as needed )

On any level ; when you come to an electric zapper in the wall, don't try to jump over them, they can be destroyed by shooting at where they attach to the wall. Another hint ; go to plugins and waste ammo you never use on them( like electric pistol ).

The way to defeat this mother fudger just climb up all the way up to the platform on top of him and then when the hole in his head throw grenades or missiles.Keep doing this and you'll defeat him in no time.
Club America rules!!!