how do you defeat the gray thats hiding behind the force field thats reacting the black ops?

you run around with the smp or shot double blast with shot gun auto with the smp till his sheild goes boom then hes dead from the blast you walk through the corridore press the button and if you have shot gun ammo pull it out and blast the "bubbles" and toss in a few jb grenades

mutate and fire parrasites at him, it breaks the shield well quickly

I tried the whole just throwing grenades but, I'm not having any luck. not only that how in the world do you stay alive long enough. I know about the supply thing to the right, but I'm still getting stomped

you just mutate then to keep the mutagen up you melee the guys behind the barricade then to keep your health up you shoot parasites on the upper floor guys

are there co-op mode in this game?

Yeah it is easier to shoot the parasites at it, it kills him quickier than weapons that you have, but the weapons will eventually kill it, but it will take awhile to do it,and a waste

shoot the force field and it will turn colors from green to yellow to re then it disappears and you can kill them.