I'm still alive!
Start the game after the crash.




Meet the Raiders
Meet the Raiders.




Clear Sky
Destroy the combine helicopter.




Successful Evacuation
Complete the walkthrough.

Strider Killer
Kill all 3 striders.



While being in the helicopter, kill the 3 striders that's attacking you.
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Leap of faith
Fall into the ravine.



After the helicopter crash you come to a camp site where you get a pistol. To the left of the camp is a cliff. Jump off the ledge and you get the achievement.
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Saving the medic
Kill the raider before he kills the rebel medic.



After you activated the first radio tower you'll come to a bridge leading over to an outpost. You need to kill all of the raiders in the outpost before they kill the rebel. Be quick and take out the raider behind the fence next to the rebel. Tip: save right before the bridge incase the rebel dies.
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Evacuation Chomsky's gnome
Bring the gnome from the sawmill to the end.



You'll find the gnome in the right building upon entering the sawmill. Take it with you to the end.
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Corps Killer
Clear the ravine of all zombies.



Near the sawmill you'll come across a ravine which has alot of zombies in it. You need to kill every zombie in the ravin, including the headcrabs.
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From Russia with love
Find the Kalashnikov assault rifle.



After you get out of the ravine, you'll come to a tent with three raiders where you find a power cable. Next to the power cable is the Kalashnikov.
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Guardian - no problem
Kill the ant lion guardian.



When the power is activated at the sawmill, an antlion guardian appears. Kill it to get the achievement.
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Rescue
Kill the bird before it sits in the trap.



After leaving the sawmill you will eventually come to a watch tower. After opening the gate at the watch tower you'll find bear traps. A bird will fly into the first bear trap, so be quick to take it out before it hits the trap.
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Get Overpowered
Die from the current in the socket.



The socket is located at the second radio tower. While the socket is charged, pick it up.
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Rocketjump!
Jump on a nearby cable car using a rocket launcher.



After leaving the second radio tower, you'll come to a cable car. For this achievement you need to launch yourself towards the cable car that's coming towards you. When you're close to the oncoming cable car, turn around and shoot the RPG at the floor of the cable car you stands in and use that momentum to fly (rocketjump) towards the cable car. You only need to touch the cable car, not land in it. But you need to use the RPG/explosive to launch yourself, otherwise you won't get this achievement. To save some time: Save before activating the cable car.
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Explorer
Find a box of supplies behind the waterfall.



After you group up with a rebel you'll come to a river filled with combines and antlions. The waterfall is located at the end of that river. Check behind the waterfall and you'll find some crates.