Hit the trashcan cop with the can.

Put the can in the trash.

Escape the apartment block raid.

Break the mini teleporter in Kleiner's lab.

Kill five barnacles with one barrel.

Get the crowbar.

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.

Get the Gravity Gun in Black Mesa East.

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

Play through Ravenholm using only the Gravity Gun.

Use Dog's ball to make a basket in the scrapyard.

Escort Grigori safely through the church cemetery.

Kill 3 enemies using the crane.

Defend Little Odessa from the Gunship attack.

Pin a soldier to the billboard in the chapter Highway 17.

Destroy six Gunships in Half-Life 2.

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

Kill an enemy with a toilet.

Use the Antlions to kill 50 enemies.

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.

Kill five enemies with a Manhack.

Survive the generator plaza standoff in the chapter Anticitizen One.

Kill all of the snipers in City 17.

Survive the rooftop Strider battle in the ruins of City 17

Shut down the suppression device by disabling its generators.

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

Destroy the Citadel's reactor core.