Here is the full list of all 50 Black Mesa achievements. It takes around 20-25 hours to unlock all of the achievements on Windows.
Complete Interloper without taking any laser damage.
View the *other* secret ending.
Carry the Hidden Hat to Endgame.
Kill all Protozoans in the Borderworld.
Don't kill any Vortigaunts in the Borderworld.
Escape the Gargantua’s Lair without taking any damage from Gargantuas.
Find the snack supply canister.
Deliver the finishing blow to Gonarch with your Crowbar.
Use Cyanogen to kill Gonarch.
Don't use the Cyanogen and let the Gonarch live.
Find each member of the missing research teams.
Get whacked into oblivion in the ledge fight.
Use the welcome mat.
Skip the opening Xen island with a secret jump.
Wait too long to jump into the Lambda Teleporter.
Escape the Hangar in Surface Tension without alerting the Soldiers.
Kill 10 Enemies with Tripmines.
Assemble all the possible Scientists and Guards at the end of Office Complex.
Cook a Grenade for too long.
Die in the AMS Beam before starting the experiment.
Decline G-Man’s offer of employment.
Accept G-Man’s offer of employment.
Defeat Nihilanth in under 4 minutes.
Take out all three Healing Crystals in Nihilanth’s Chamber at the same time.
Kill a Controller without killing any of its mind-controlled Vortigaunt slaves.
Send the Hidden Hat to Xen.
Drown in Lambda Core's coolant.
Use an entire clip of Gluon ammo in one continuous shot.
Kill 20 enemies with the Hivehand.
Kill an Icthyosaur with either the Tau or Gluon.
Conduct all of the questionable research experiments.
Overcharge it anyway.
Kill 10 enemies with Snarks.
Get killed by your own Snarks.
Help the Barnacle and Headcrab find true love.
Kill an Assassin with the .357 Magnum.
Kill a Headcrab using fire.
Kill 10 Airborne Headcrabs using the Shotgun.
Kill a Barnacle with a Satchel.
Kill a Marine with their own grenade.
Headshot 20 enemies with the .357 magnum.
Kill 10 enemies with a reprogrammed Sentry.
Use the alternate path in Office Complex.
Kill 5 enemies with one grenade.
Get overtaken by a Headcrab's ample anterior.
Perform surgical caffeine extraction from 20 machines.
Refuse to insert the specimen into the Anti-Mass Spectrometer.
Pass the toilet paper to the scientist in need.
Ruin the microwave casserole.
Interfere with the alarm and laptop in Anomalous Materials.