You need to have the AA-12 Auto Shotgun with full ammo and Full Armor.

You're going to be using your AA Auto Shotgun througout the whole fight, you won't run out of ammo if you follow these instructions.

1. Empty your magazine on the boss, it doesn't necessarily have to be headshots, although it would be nice.

2. When you've emptied your mag on the boss you should see him change his colors, this is the part when he will throw down white smoke bombs. At the time you see him change colors or throw down the smoke bombs you must reaload your shotgun. Just back away while reloading.
^

3. After you've reloaded your shotgun you should let him charge at you and drain you. When he's done draining you he will become stunned for a short amount of time, this is when you should empty your mag on his head. Move closer to him if you feel the need. Don't forget to heal yoursef too, you should have time to heal yourself after headshotting him if you do it quick enough and continue to back away.
^

4. At this time he should change his colors again throwing down white smoke bombs, just repeat step 2 and step 3 above.

5. Rince & Repeat. :)

This may sound like a long bossfight but trust me haha it truly is not. ^^

You can try this trick using the Berserker class too with the sledgehammer's righ-click attacks. I'm quite sure it should work.

Please make sure to like if you found this helpful!! :)