Beat the game in 2-player co-op on any difficulty.
Defeating Cobar
Run and the grab the missile launcher from the supply depot at the bottom left of your screen. While hiding behind the concrete block next to the depot, throw grenades at his machine gun. This enables you to lock on to his missile launchers (which cause the most havoc). In order to lock on to one weapon at a time, hold L + R while firing or throwing grenades. Once enough damage has been done with the grenades, his missile launchers will turn so that you may see the holes. You can now lock onto them. From this position, shoot the left one first. Fire two rockets as fast as possible and make sure that you do not miss. If you miss, restart. After both rockets hit the left missile launcher, you must run around a bit. Make sure that you reload after the first two shots. In between the rockets that he shoots at you, aim at his right missile launcher and get both shots off. This may be easiest from either the tall cement pillar or the small cement block on the right, as neither barrier breaks down after wear. In any case, do whatever is needed to kill the second missile launcher. You may relax a little bit now, as he cannot hit you if you are behind one of the cement barriers. Either grab the sniper rifle or the crossbow that you brought with you (if over ten shots remain), and go to the cement barrier by the left supply depot. While holding L + R, hide behind the barrier and focus on the mine thrower on the top of the machine or the machine gun that is tearing you up. Time your shots so that you are hiding while he is shooting and you are shooting while he is reloading. Try to destroy this weapon as fast as possible. It may just happen that the Spider Mines start climbing out before you are finished with the weapon at hand. As soon as you see the Spider Mines climbing out, run to the supply depot and get the assault rifle (or counterpart) and immediately lock on to the spider mines that are coming towards you. Only about five are released at a time, but you must kill them while they close to the Boss so that they do not explode near you. Tap L(2) to roll out of the way if they are about to explode near you. Try to kill the Spider Mine hatch now, before more come out. After you kill the left, run to the other side, as more Spider Mines will also come out of there. Repeat the previous step then kill off this side as well. Go back to the left cement barrier, refueling any life that may have been lost. If you are hiding from the machine gun, get directly behind the barrier. If you are hiding from the mine thrower, get to the back right corner of the barrier, but directly up next to it. Get out of the way of the explosions or bullets. Time your shots in between his and take out the remaining guns.
Defeating General Metrac
The first area is mostly self-explanatory. Just keep shooting at him (preferably with the revolver), and toss grenades to force him out of hiding. After he loses enough health, he will toss a smoke grenade and run away. Grab any supplies and take the M82 or keep the revolver. The second area is slightly wider. Metrac will run around on a catwalk to the right and top. Shoot the valves on the right side when he is over there. Fire will shoot out of the valve for awhile, blocking off that area from Metrac. It is best to trap him on the right or in between the two fire jets (use the object lock). Metrac will retreat again after taking too many shots and go into a third area. Resupply, then follow him. For the third area, it is best to use the M82 just because it fires more shots. and in the third area you don't have much time to be precise. Metrac is in a mounted machine gun turret, which is heavily armored. You could sit there and shoot at the turret, but you would probably run out of ammunition (although you can destroy the turret this way). Instead, shoot the generators on either side. Throw grenades at them first, then finish them off with the M82. Do the same for the other generator. The gun will power down and Metrac will get out. He will then do the same little dance he did in the other two areas: fire some shots, then launch grenades, reload, and repeat. Proceed to shoot him the same way you did before, but be careful. All the boxes except the ammo boxes and the two crates that are directly in front of you can be destroyed. When he is launching grenades, wait until the grenade is in the air, then move. This will cause the grenade to land in your previous location and not hurt you. Repeat this strategy and you should eventually win.
Defeating giant Helghast
On the last chapter, you will encounter some huge Helghast that have riot shields and electric clubs. Be careful, as two hits from that club kills you. The best way to kill them is with heavy weaponry. Rocket launchers would be good, but there will not be any around the first time you encounter them. The Helghast Chaingun works fine, however. If you shoot at them enough, eventually you will hit them in the head and they will fall. This lets you shoot them while they are down. Alternately, run around crates and boxes until you can sneak up behind them, then rip up their back with the chaingun. Additionally, when you have the mini-Boss fight with the Colossal Helghast, the chaingun is the best weapon to use against him. Do not overheat it too much; fire in short bursts.
Metrac
Beat Easy, Normal, and Hard modes.
Specialist
Win 10 games in Ad-Hoc or Infrastructure Multiplayer.
Stratson
Win 100 times in MP(ad-hoc or infrastructure).
Unlock Concept art pack #1
Finish Single Player Campaign 3-4 on Normal.
Unlock Indepth character profiles #1
Finish Single Player Campaign 1-1 on Easy.
Unlock Indepth character profiles #4
Finish Single Player Campaign 4-4 on Easy.
Unlock Jukebox
Finish Single Player Campaign 2-4 on Normal.
Unlock Multiplayer Character: Cobar
Finish Single Player Campaign 4-4 on Hard.
Unlock Multiplayer Character: Evelyn
Finish Single Player Campaign 4-4 on Normal.
Unlock Wallpaper pack #1
Finish Single Player Campaign 1-4 on Easy.
Unlockable abilities
You can access the ability selection screen by pressing square on the weapon selection screen. Abilities are unlockable bonuses that let you do certain things, like carrying 3 grenades or having 50% more health. You can unlock these abilities by aquiring a certain amount of points. Points can be collected by completing challenges.
Effect - Code
Unlock 50% More health - 300 Points
Unlock C4 Placement twice as fast - 100 Points
Unlock Carry 3 Grenades - 020 Points
Unlock Carry 3 Smoke grenades - 140 Points
Unlock Carry 3 Syringes - 060 Points
Unlock Carry 4 Pressure Mines - 220 Points
Unlock Carry Unlimited ammunition - 480 Points
Unlock Close Combat damage doubled - 260 Points
Unlock Trip Mines disarmed twice as fast - 180 Points
Unlock Your Buddy has 50% more health - 340 Points
