Thing, The

Pay very close attention to your team. If you see someone doing odd things, such as not shooting at enemies when they appear, or moving rather far away from you when your walking, be on alert as this could be a sign of infection. However, do not waste a Blood Test Kit on him to see if you are correct. Just be on alert because they could mutate at any second. This also goes for you as well -- if your team sees you doing the same things, they will question your trust and may attack you.

Save Blood Test Kits for showing your team that you are not infected to gain trust. Using them on a team member is useless because they get infected randomly, and usually break out within a minute of infection.

Go into to his garage. Fix the electrical panel that operates the hoist. Step back towards the middle of the big door. There is an opening between two of the crates. Using your grenade launcher in first person targeting, send in a grenade. If the Thing turns its head toward you, then you have him targeted. Continue sending in grenades until he begins to burn. You can send in a few more if desired for extra fun. Run into the Thing's room and on the far wall from the big door is a switch. Throw the switch and watch as the Thing dies. You will probably take one hit from him.

Run around the Boss in a circle while shooting it with the machine gun. When it is low on health, use the flame thrower to finish it off. If done correctly, you can kill it without being hit. After you kill the Boss, the Thing in the glass in the room will break out, and the door will be opened with a few guards.

Use the following trick to get a doctor in the same room with you during your battle with the second giant Thing. Walk to the large garage door. Get the doctor close to the door as well. Then, tell him to not follow you anymore. Push him as close to the door as possible; and close enough to you that when you flip the switch to open the door he will not move. Before you flip the switch, tell him to follow you again. Flip the switch and when you are shown in the locked room with the second giant Thing, he should be beside you. Use him to heal you during the fight with the Thing.

The following trick requires Stun Grenades (found in the back of the room with Boss 3), Blood Test Kit (found in the same room), and the Grenade Launcher (in the save room down the hall from Boss 3). Starting after third Boss fight (hanging tentacle monster), backtrack your way out of the weapons lab, back up the air vent, and to the "mine" elevator. As soon as you reach the surface, strafe left, and equip both the Grenade Launcher and Stun Grenades. If you step forward at all, it triggers an intermission sequence you have to die and start the level over. Enter first person mode and aim up the corridor, parallel with the bottom of the last metal wall panel. Launch a grenade and quickly walk forward. The intermission sequence will trigger, but Whitley will stand still instead of running off. Now, quickly run ahead of him (preferably block his path to slow him down) and use the Blood Test Kit. He now trusts you enough to follow orders. Order him to follow you (otherwise he walks around the corner triggering guards to attack) and give him a weapon. You have now backup. He only lasts a brief amount of time, and will disappear roughly halfway up the snow corridor, which appears scripted. However, every bit of backup firepower helps in that spot.

Before entering the room with Boss 3, push your engineer towards the door until it opens. Then with the door open and your engineer between you and the doorway, take one last step to enter the room and you will push your engineer in too. He will attack the Boss for you and the Boss will attack him instead of you. Until he's dead, that is.

Variants:
Take a couple steps back before pushing the engineer through the door and run at him. Instead of pushing him all the way into the room, you'll go through him and he will stay outside but his face and gun will be visible through the door and he'll still attack the Boss briefly.
Also, if you do this, the door may stay open for the cutscene, during which the engineer will attack through the door. When I did this, he had a shotgun and you could see blood spraying from the back of my head with each shot during the cutscene but it did no damage to me. Not sure if having the engineer attack during the cutscene does damage to the Boss.

Wait about one minute at the main menu to view a longer, uncut television trailer for the game.

Listen to your team. They will tell you how they feel. If you hear someone say something similar to "We're gonna die", check the team menu and see how he is doing. If there is an X across his face while he is shaking uncontrollably, bring out the Tazer and shock him. Wait for him to calm down, move out of the area, and give him back his gun. He might be bitter, but after you kill a few more things he will be fine. Otherwise, he might start shooting you and your team, ending with himself in the head.

Before you enter the room where you meet Boss 3, push your engineer towards the door until it opens. You will be able to look into the room without the Boss Battle starting. From there you can shoot the tank holding the walker and he will come out to attack you. Get him out and you can kill him. Then when the Boss Battle starts you will have one less Thing to think about.