In the first battle, equip your rifle and as soon as you get the chance, shoot him four times. He will run away. Follow him into the next room. Get far away from him and just keep shooting until he dies. If he gets in close, run away and shoot him. If done correctly, he should be locked in between shots and you will not get hit.
Game Shark Codes
Master Code (Must Be On) EC8DBED0 14431F04
Infinite Health 4CA9F29A 145625DD4CA9F2A2 145625DD