No missable achievements (plus 33 unknown)
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Escape the apartment block raid.
Get the crowbar.
Get the airboat.
Kill five barnacles with one explosive barrel.
Get the airboat's mounted gun.
Destroy the Hunter-Chopper.
Get the Gravity Gun in Black Mesa East.
Use the Antlions to kill 50 enemies.
Gain command of a squad of rebels in the uprising.
Survive the second turret standoff in Nova Prospekt.
Destroy six gunships in Half-Life 2.
Get through the toxic tunnel under City 17 in Half-Life 2.
Survive the generator plaza standoff in chapter Anticitizen One.
Kill 3 enemies using the crane.
Shut down the supression device by disabling its generators.
Survive the rooftop strider battle in the ruins of City 17.
Break the mini-teleporter in Kleiner's Lab.
Pin a soldier to the billboard in the chapter Highway 17.
Kill all of the snipers in City 17.
Find the HEV Suit Charger faceplate in Eli's scrapyard.
Discover the hidden singing vortigaunt cave in chapter Water Hazard.
Disintegrate 15 soldiers by throwing them into a Combine ball field.
Use Dog's ball to make a basket in the scrapyard.
Kill an enemy with a toilet.
Play through Ravenholm using only the Gravity Gun.
Kill five enemies with a Manhack.
Cross the antlion beach in chapter Sandtraps without touching the sand.
Find all lambda caches in Half-Life 2.