A lot of this list is single-run conditions that don’t conflict with each other, so you can earn several at once instead of replaying for each. Each plan below is one run. Achievements in a plan are marked with a ⛓ badge further down.
Play from the start of Xen through the end of Interloper in one continuous save, with the crossbow ready. Spare every Vortigaunt, pop every Protozoan you see, avoid all laser damage in Interloper, and take no hits from the Gargantuas in their lair.
- ✓▢PhD in Pacifism — Don't kill any Vortigaunts in the Borderworld.
- ✓▢Prolific Popper — Kill all Protozoans in the Borderworld.
- ✓▢Laser Immunization — Complete Interloper without taking any laser damage.
- ✓▢Black Mesa Decathlon Winner — Escape the Gargantua’s Lair without taking any damage from Gargantuas.
- ✓▢Anti-Matter Over Mind — Kill a Controller without killing any of its mind-controlled Vortigaunt slaves.
- ✓▢Contest Propellant — hidden achievement; Steam publishes no description
PhD in Pacifism and Laser Immunization both unlock at the summit of the Alien Grunt factory in Interloper (Combine OverWiki). Prolific Popper spans Xen, Gonarch's Lair and Interloper (37 + 22 + 5 Protozoans), so a missed one early means replaying those chapters. Anti-Matter Over Mind fits naturally: a crossbow headshot on a Controller also keeps its Vortigaunts alive for PhD in Pacifism. Not verified whether starting Interloper from chapter select keeps the Borderworld-wide ones valid - play straight through to be safe.
Pick up the cyanogen canister at the Xen research outpost and carry it into Gonarch's Lair. The last missing research-team body needs the canister with you, and The Plan needs you to gas Gonarch with it.
- ✓▢Post-Mortem Interval — Find each member of the missing research teams.
- ✓▢The Plan — hidden achievement; Steam publishes no description
- ✓▢Gonad Glider — Get whacked into oblivion in the ledge fight.
CONFLICT: Unquestionably Ethical needs you to carry the canister in and NOT use it, letting Gonarch live - the direct opposite of The Plan. Doctor’s Signature needs a crowbar killing blow, which may not be compatible with a cyanogen kill (not verified). Save when you enter the lair and reload for each ending. Gonad Glider (get kicked off the ledge in the first fight) is a free death to take before the real attempt.
Arrive at Nihilanth with at least three satchel charges and full heavy-weapon ammo. Satchel all three healing crystals and detonate at once, then burn Nihilanth down inside four minutes.
- ✓▢Specimen GG — Take out all three Healing Crystals in Nihilanth’s Chamber at the same time.
- ✓▢Late for Work — Defeat Nihilanth in under 4 minutes.
Destroying the crystals early is what makes the four-minute clock realistic, so these two help each other. The item carries (The Rarest Specimen, Pepperoni Precipitation) also end at this fight - whether you can carry the hat and the pizza box at the same time is not verified.
Early in Anomalous Materials, a scientist is stuck in a washroom stall and needs a roll. Pick up a toilet roll (or paper towels) and hand it to him through the stall - the Combine OverWiki notes either item works. Black Mesa has chapter select, so if you miss it you can reload the chapter rather than replaying the game.
In Anomalous Materials, find the microwave with a casserole in it and press its button. Leave it running - it overheats after a while and the achievement pops. Black Mesa has chapter select, so if you miss it you can reload the chapter rather than replaying the game.
20 Magnum headshots, cumulative. Humans and Marines are the easiest targets, since their heads are obvious and they don't leap around. Use the Magnum for opening shots on unaware enemies.
Be killed by a Headcrab. Any Headcrab from Unforeseen Consequences onward counts - drop your health low and let one land on you, then reload.
In Interloper, kill a Controller while its enslaved Vortigaunts survive. The wiki recommends a single crossbow headshot on the Controller.
Fill the Gluon Gun to its full 100 units and hold fire without letting go until it's empty.
From Unforeseen Consequences onward, pick up a flare and throw it at (or hold it against) a Headcrab until the fire alone kills it. Don't finish it with your crowbar or a gun, or the kill won't count as fire.
At the end, step into the portal after the G-Man finishes his speech. Save before Endgame so you can also do Rather an Anticlimax.
In Office Complex, look for a meeting room with overturned furniture. A ladder there leads up into the ceiling vents; crowbar the ceiling tiles out of your way and follow that route instead of the main path. Black Mesa has chapter select, so if you miss it you can reload the chapter rather than replaying the game.
Female Black Ops Assassins appear in Apprehension and Lambda Core per the wiki. They're fast and flip around, so wait for them to land or close in, then land Magnum shots. The killing blow must be the Magnum.
20 kills with the Hivehand, cumulative from Surface Tension onward. It recharges its own ammo, so use it freely on weak enemies.
Press the button on soda vending machines until cans drop - 20 in total. The wiki lists eligible machines from Anomalous Materials through Forget About Freeman, so just use every machine you pass early on.
Once you have frag grenades, hold alt-fire to pull the pin and just keep holding until it explodes in Gordon's hand. Save first - it will very likely kill you.
Five kills from a single grenade. The Combine OverWiki suggests a hallway where five barnacles hang close together: throw a grenade onto the tongue of the middle one so the blast catches all five. Any tightly packed group works if you find a better spot.
Hold the Tau Cannon's alt-fire and keep holding past full charge. It overloads and hurts you - save first, then just keep holding.
At the end, don't step into the portal. Wait about 20 seconds after it opens. Reload your save to also take Limitless Potential.
Both halves are in Anomalous Materials: use the laptop to the left of the security door, and press the alarm button under the guard's desk. The Combine OverWiki lists this pair as the trigger. Black Mesa has chapter select, so if you miss it you can reload the chapter rather than replaying the game.
In the test chamber in Anomalous Materials, jump into the Anti-Mass Spectrometer beam once it comes online, before you push the specimen in. You die, the achievement pops, reload. Save first. Black Mesa has chapter select, so if you miss it you can reload the chapter rather than replaying the game.
Shoot Headcrabs out of the air mid-leap with the shotgun, 10 times. Wait for the jump, then fire - point blank works best. Cumulative, so it will come over time once you commit the shotgun to Headcrab duty.
Lure an Ichthyosaur up out of the water - stand near the edge - and hit it with the Tau Cannon or Gluon Gun before it dives again. Available from Surface Tension onward.
Don't kill any Vortigaunts throughout the Xen chapters. It unlocks when you reach the summit of the Alien Grunt factory in Interloper. Aim carefully in fights where Vortigaunts are mixed in - splash damage counts.
Once you have satchel charges (from Blast Pit onward per the wiki), throw one onto a Barnacle's tongue - it pulls the satchel up - then detonate.
In Surface Tension, get through the hangar section without any soldier detecting you. Move slowly, stay out of sight lines and save before the hangar so you can retry each attempt. Black Mesa has chapter select, so if you miss it you can reload the chapter rather than replaying the game.
Hidden on Steam. In Interloper, after the Controller battle in the Vortigaunt village, go through a vent and break the boxes on the left to reveal a passage. The canister is at the end of it.
Release Snarks with no other targets nearby and let them turn on you. Save first.
In the same test chamber, simply don't push the specimen cart into the beam. After roughly a minute the machine overcharges and kills Gordon - that's the unlock. Save before the chamber so you can do this and Less Than Desirable Consequences back to back. Black Mesa has chapter select, so if you miss it you can reload the chapter rather than replaying the game.
From We've Got Hostiles onward, approach an idle sentry gun from behind, pick it up and redeploy it facing your enemies. Its kills count toward the 10.
Throw Snarks at groups of enemies - kills they score count. Cumulative from Questionable Ethics onward.
Let 10 Headcrabs get grabbed by Barnacles. The wiki recommends the conveyor-belt section in We've Got Hostiles, where Headcrabs ride past Barnacles repeatedly - wait there until the count fills.
Place tripmines where enemies will walk through the beams - they can also be set off by shooting them or with a satchel. Cumulative across the game from Power Up onward.
When a Marine throws a grenade at you, pick it up and throw it straight back. The Marine who threw it must be the one it kills. Available from We've Got Hostiles onward.
In Lambda Core, dive into the coolant water and stay under until you drown. Save first. Black Mesa has chapter select, so if you miss it you can reload the chapter rather than replaying the game.
In the first Gonarch encounter on the ledges, let Gonarch kick you off into the abyss. Save first. Black Mesa has chapter select, so if you miss it you can reload the chapter rather than replaying the game.
Bring 4 security guards and 2 scientists (one man, one woman) alive to the elevator shaft at the end of Office Complex - that's the requirement the Combine OverWiki gives. Escort each one carefully: they wander into fire, so clear rooms ahead of them first and save often. Black Mesa has chapter select, so if you miss it you can reload the chapter rather than replaying the game.
In Questionable Ethics, use the lab equipment itself (not your guns) to kill an Alien Grunt, Snarks, a Bullsquid and Headcrabs - four separate experiments. Each lab has its own apparatus; interact with the controls when the specimen is inside. Black Mesa has chapter select, so if you miss it you can reload the chapter rather than replaying the game.
Hidden on Steam. At the end of Lambda Core, when the portal to Xen opens, don't jump in. After about a minute it overloads and kills Gordon, which unlocks this. Save before the teleporter and do this first, then reload and jump.
Hidden on Steam. In Xen, after the blue cavern lake, the research habitat has a mat at its entrance. Crouch on it and press use. Black Mesa has chapter select, so if you miss it you can reload the chapter rather than replaying the game.
At the very start of Xen, instead of heading down the obvious left path, make a series of tricky jumps across the rocks to the right. Save before each jump - Xen's low gravity makes the arcs longer than you'd expect. Black Mesa has chapter select, so if you miss it you can reload the chapter rather than replaying the game.
In Interloper's Gargantua section, avoid any damage from the Gargantuas. Damage from other creatures doesn't void it. Save before the area and retry until it's clean.
Kill Nihilanth within four minutes. Go in with full ammo for your heaviest weapons and deal with the crystals quickly.
Get Gonarch to its last sliver of health with guns, then switch to the crowbar for the killing hit. Save often near the end of the fight.
In the Nihilanth fight, place a satchel charge beside each of the three healing crystals and detonate them all at once. Bring at least three satchels into the fight.
Find the purple Hidden Hat (from Unforeseen Consequences onward) and carry it all the way to the Lambda Core, then jump into the Xen portal holding it. Exact location not verified here - see a community guide. Plan this before you start, because it's a long carry.
Hidden on Steam. In Xen, pick up the cyanogen canister from the research outpost and carry it into Gonarch's Lair, then deploy the gas on Gonarch. Conflicts with Unquestionably Ethical - save before the fight to get both.
Take no laser damage across Interloper. It unlocks at the summit of the Alien Grunt factory. Save often - chapter select only resets you to the start of the chapter.
Hidden on Steam. Carry the cyanogen canister into Gonarch's Lair but don't use it, and leave with Gonarch unharmed. This is the opposite of The Plan - reload a save before the fight to do the other one.
Find all 7 HEV-suited scientist bodies in Gonarch's Lair - pick up their supplies, interact with them or crouch on them. The wiki notes the last body needs the cyanogen canister with you, so bring it along.
Hidden on Steam. Carry the hat through Xen too, all the way to the Nihilanth fight. Long carry - don't drop it.
Kill every Protozoan in Xen - the wiki counts 64: 37 in Xen, 22 in Gonarch's Lair and 5 in Interloper. They're the floating creatures; one missed means replaying, so sweep each area thoroughly.
Hidden on Steam. In Questionable Ethics, find Dr. Horn's pizza box in the cafeteria, carry it to Xen, and then carry it all the way to Nihilanth. Same idea as the Hidden Hat, with a different object and ending.
