Continue playing to unlock this secret achievement.
Kill an Elite Soldier with his own energy ball.
Disintegrate 15 soldiers by throwing them into a Combine ball field.
Survive the rooftop strider battle in the ruins of City 17.
Destroy six gunships in Half-Life 2.
Shut down the supression device by disabling its generators.
Kill all of the snipers in City 17.
Survive the generator plaza standoff in chapter Anticitizen One.
Get through the toxic tunnel under City 17 in Half-Life 2.
Gain command of a squad of rebels in the uprising.
Break the mini-teleporter in Kleiner's lab.
Survive the second turret standoff in Nova Prospekt.
Win 2Fort with a shutout.
Accumulate 10 turret kills with a single turret.
Beat DOG in a race to the White Forest base.
Find every radar cache in chapter Under The Radar.
Unlock the rocket launcher lambda cache in chapter Under The Radar.
Run over 20 enemies with the car in Episode Two.
Help Griggs and Sheckley hold off the antlion invasion inside the mine shaft.
Kill an acid antlion worker.
Beat Episode One firing exactly one bullet. Grenade, crowbar, rocket, and Gravgun kills are okay!
Escape City 17 with Alyx.
Don't let any citizens die when escorting them to the escape train.
Kill five enemies with a Manhack.
Kill an enemy by planting a hopper mine.
Destroy the gunship in the hospital attic.
Kill a Combine soldier with his own grenade.
Survive long enough to get on the parking garage elevator.
Steal a Zombine's grenade.
Contain the Citadel core without killing any stalkers.
Contain the Citadel core.
Make it to the bottom of the Citadel's main elevator shaft in one piece.
Get five kills in a row without dying.
Kill an enemy with a toilet.
Use the antlions to kill 50 enemies.
Kill 3 enemies using the crane.
Knock down a turret with another turret.
Play through Ravenholm using only the Gravity Gun.
Kill 30 enemies with thrown physics objects.
Find the HEV Suit Charger faceplate in Eli's scrapyard.
Use DOG's ball to make a basket in Eli's scrapyard.
Get the Gravity Gun in Black Mesa East.
Destroy the hunter-chopper in Half-Life 2.
Fall 30,000 feet.
Get the airboat's mounted gun.
Get the airboat.
Get the crowbar.
Complete Portal.
Make the correct party escort submission position decision.
Escape the apartment block raid.
Do whatever it takes to survive.
Acquire the fully powered Aperture Science Handheld Portal Device.
Defeat the chopper in Episode Two without any misses.
Send the garden gnome into space.
Save all buildings outside the missile silo from destruction.
Kill a Hunter with its own flechettes.
Jump 300 feet.
Beat two Portal advanced maps.
Beat four Portal advanced maps.
Beat all six Portal advanced maps.
Earn bronze medals on all Portal challenges.
Earn silver medals on all Portal challenges.
Earn gold medals on all Portal challenges.
Get five revenge kills.
Trick an opposing medic into healing you.
Play in a game with seven or more players from your friends list.
Win 20 games.
Accumulate 1000 total kills.
Win Well in 5 minutes or less.
Win Hydro without giving up a capture.
Successfully defend Dustbowl without giving up a capture.
Successfully defend Gravel Pit without giving up a capture.
Play a complete round with every class.
Play a complete game on every map.
Accumulate 25000 heal points as a Medic.
Set five enemies on fire in 30 seconds.
Get 25 headshots as a Sniper.
Detach security cameras from the walls.
Kill five enemies with the same energy ball.
Use flares to light 15 zombies on fire.
Kill five barnacles with one barrel.
Discover the hidden singing vortigaunt cave in chapter Water Hazard.
Pin a soldier to the billboard in chapter Highway 17.
Cross the antlion beach in chapter Sandtraps without touching the sand.
Find all lambda caches in Half-Life 2.
Use the cars to squash 15 antlions in Episode One.
Help Alyx snipe 30 enemies in Episode One.
Squish every antlion grub in Episode Two.
Find and break every web cache in Episode Two.
