Easy way to beat gas mask guy!
I take absolutely no credit for this. I was thumbing around on youtube and I was watching the walkthrough for this game. I noticed a comment that read "It is better to knife him, he goes down faster and easier." I decided to try it (on hard mode), and it WORKED!!! All you have to do is when you start the battle with the gas mask guy, is take out your knife (I used the machete), and run up to him. Then just keep hitting right trigger like crazy!!! You might die the first time, but once you know where to look when you are swinging away, it takes maybe about a minute or two. So simple. Have fun!