Achieve the rating: Silent Assassin
Unlock a technique
Continue playing to unlock this secret achievement.
Achieve your first accident kill
Subdue a person
Blend in successfully
Hide a body
Hold the Platform without dying.
Fall in the Swamp 10 times.
Complete the BRIDGE level without a kill.
Kill 100 Mutants.
Install all possible Customizations for a Weapon.
Kill 100 Human Enemies.
Make 10 Spiders flip belly-up.
Turn off 40 Lights without breaking them.
Stealthily kill 15 Enemies.
Write 10 of Artyom's hidden Diary pages.
Complete the ECHOES level undetected by the Watchmen.
Escape the chasing Nazis on the REICH level without being caught once.
Complete training sequence.
Take GLaDOS' escape advice
Break the rules in Test Chamber 07
25 enemies know the power of magic from their graves
Did 20 10x combos!
Sent a curse or blessing to another player
Killed 25 enemies
Created first Caos
Taunt GLaDOS in front of a camera in each of the five co-op courses
Beat the game on any difficulty.
Kill 500 aliens.
Make contact with the Ethereal hive mind.
Build the Gollop Chamber.
Staff the Engineering Department with 80 engineers
Staff the Research Labs with 80 scientists.
Gain access to the lowest level in your base.
In a single game, complete every Autopsy.
Successfully assault an Overseer UFO.
Acquire 1000 credits in one month.
Earn the "Excellent" rating in every performance category on a terror mission.
Build a Firestorm.
Build a suit of powered armor.
Recover the Hyperwave Beacon.