Hot Potat0wned
Kill a Combine soldier with his own grenade.
Payback
Kill a Hunter with its own flechettes.
Cache Checker
Find every radar cache in chapter Under The Radar.
Gordon Propelled Rocket
Unlock the rocket launcher lambda cache in chapter Under The Radar.
Grave Robber
Steal a Zombine's grenade.
Bone Breaker
Kill 30 enemies with thrown physics objects.
Deadly Harvest
Kill an enemy by planting a hopper mine.
Live Bait
Help Alyx snipe 30 enemies in Episode One.
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.