Accept G-Man’s offer of employment.
Don't kill any Vortigaunts in the Borderworld.
Kill a Controller without killing any of its mind-controlled Vortigaunt slaves.
Kill an Ichthyosaur with either the Tau or Gluon.
Overcharge it anyway.
Headshot 20 Enemies with the .357 Magnum.
Kill an Assassin with the .357 Magnum.
Use the alternate path in Office Complex.
Pass the toilet paper to the Scientist in need.
Ruin the microwave casserole.
Take out all three Healing Crystals in Nihilanth’s Chamber at the same time.
Get whacked into oblivion in the ledge fight.
Assemble all the possible Scientists and Guards at the end of Office Complex.
Die in the AMS Beam before starting the experiment.
Skip the opening Xen island with a secret jump.
Deliver the finishing blow to Gonarch with your Crowbar.
Find each member of the missing research teams.
Decline G-Man’s offer of employment.
Defeat Nihilanth in under 4 minutes.
Escape the Hangar in Surface Tension without alerting the Soldiers.
Complete Interloper without taking any laser damage.
Escape the Gargantua’s Lair without taking any damage from Gargantuas.
Kill all Protozoans in the Borderworld.
Kill 10 Enemies with Tripmines.
Kill 5 Enemies with one Grenade.
Kill 10 airborne Headcrabs using the Shotgun.
Kill 20 Enemies with the Hivehand.
Kill 10 enemies with a reprogrammed Sentry.
Conduct all of the questionable research experiments.
Kill 10 Enemies with Snarks.
Drown in Lambda Core's coolant.
Kill a Headcrab using fire.
Kill a Marine with their own Grenade.
Use an entire clip of Gluon ammo in one continuous shot.
Get overtaken by a Headcrab's ample anterior.
Interfere with the alarm and laptop in Anomalous Materials.
Send the Hidden Hat to Xen.
Kill a Barnacle with a Satchel.
Refuse to insert the specimen into the Anti-Mass Spectrometer.
Help the Barnacle and Headcrab find true love.
Get killed by your own Snarks.
Perform surgical caffeine extraction from 20 vending machines.
Cook a Grenade for too long.