Escape the apartment block raid.

Break the mini-teleporter in Kleiner's lab.

Get the crowbar.

Kill five barnacles with one barrel.

Get the airboat.

Get the airboat's mounted gun.

Discover the hidden singing vortigaunt cave in chapter Water Hazard.

Destroy the hunter-chopper in Half-Life 2.

Find the HEV Suit Charger faceplate in Eli's scrapyard.

Get the Gravity Gun in Black Mesa East.

Use DOG's ball to make a basket in Eli's scrapyard.

Play through Ravenholm using only the Gravity Gun.

Escort Gregori safely through the church cemetery.

Kill 3 enemies using the crane.

Pin a soldier to the billboard in chapter Highway 17.

Defend Little Odessa from the gunship attack.

Destroy six gunships in Half-Life 2.

Cross the antlion beach in chapter Sandtraps without touching the sand.

Use the antlions to kill 50 enemies.

Kill an enemy with a toilet.

Survive the second turret standoff in Nova Prospekt.

Gain command of a squad of rebels in the uprising.

Get through the toxic tunnel under City 17 in Half-Life 2.

Survive the generator plaza standoff in chapter Anticitizen One.

Kill all of the snipers in City 17.

Shut down the supression device by disabling its generators.

Survive the rooftop strider battle in the ruins of City 17.

Disintegrate 15 soldiers by throwing them into a Combine ball field.

Destroy the Citadel's reactor core.

Find all lambda caches in Half-Life 2.

Kill five enemies with a Manhack.