Zombie-que
Use flares to light 15 zombies on fire.
Car Crusher
Use the cars to squash 15 antlions in Episode One.
Pacifist
Contain the Citadel core without killing any stalkers.
Keep Off the Sand!
Cross the antlion beach in chapter Sandtraps without touching the sand.
Counter-Sniper
Kill all of the snipers in City 17.
Atomizer
Disintegrate 15 soldiers by throwing them into a Combine ball field.
Hack Attack!
Kill five enemies with a Manhack.
Targetted Advertising
Pin a soldier to the billboard in chapter Highway 17.
Zombie Chopper
Play through Ravenholm using only the Gravity Gun.
Flushed
Kill an enemy with a toilet.
Two Points
Use DOG's ball to make a basket in Eli's scrapyard.
Blast from the Past
Find the HEV Suit Charger faceplate in Eli's scrapyard.
Vorticough
Discover the hidden singing vortigaunt cave in chapter Water Hazard.
What cat?
Break the mini-teleporter in Kleiner's lab.
Watch Your Head!
Make it to the bottom of the Citadel's main elevator shaft in one piece.
Containment
Contain the Citadel core.
Elevator Action
Survive long enough to get on the parking garage elevator.
Attica!
Destroy the gunship in the hospital attic.
Citizen Escort
Don't let any citizens die when escorting them to the escape train.
Escape From City 17
Escape City 17 with Alyx.