Portal 2

Story-forced, in the finale. When Wheatley's reactor tips into meltdown and the manual override kicks in, survive it - which you do just by playing the ending out. See The Part Where He Kills You and Lunacy for the other two endgame pops.

Early story beat, unmissable. Pops in Chapter 2 when you plug GLaDOS's core back into her body and she wakes up and recognises you - the immortal "Oh... It's you." Just play on.

Story-forced. Pops the moment you finish the first Thermal Discouragement Beam (laser) test chamber in the early single-player chambers. You can't progress past it, so it's completely unmissable - just play on.

Story-forced. Unlocks when you complete the first Hard Light Bridge test chamber. Nothing to do but play through it.

Story-forced. "Make a break for it" pops during the Chapter 6 sabotage, when the plan turns on you and you have to leg it out of the chamber. Just play the sequence through.

Story-forced. During the core-transfer sequence the announcer needs a "Stalemate Associate" to press the emergency button nobody's supposed to press. That's you - walk up and press it. Can't be missed.

In co-op Calibration, once you and your partner clear the intro course, GLaDOS prompts you both to celebrate - throw the high-five gesture at each other and time it so your hands actually meet. Coordinate the moment with your partner and it pops. First thing you'll do together in co-op.

Story-forced. Complete the first Repulsion Gel test (the blue gel you bounce on) and it pops. Can't be missed on the way through.

Story-forced. Pops in Chapter 7 when you pick up PotatOS - GLaDOS reduced to a potato battery - and carry her onward through old Aperture. Unmissable, carrying science (literally) forward.

Story-forced. Complete the first Propulsion Gel test (the orange speed gel) and it unlocks. Unmissable as you play through.

Story-forced. Complete the first Conversion Gel test - the white gel that turns any surface portalable. Comes automatically as you play through old Aperture.

In Chapter 8, once Wheatley's running the place, he proudly shows off a test he designed himself - a stupidly simple one. Solve it, and he's so chuffed he asks you to do the exact same test again. Do it a second time and this pops - the same test twice.

Clear every chamber in the first co-op course, Team Building. It's the opening course and there's no way to progress in co-op without finishing it, so just play through it with your partner.

Story-forced. Complete the first Excursion Funnel test (the tractor-beam tube you ride) and it pops. Just part of playing through.

Story-forced. This is literally the part where he kills you - it pops during the final Wheatley boss fight, right as the chapter card bearing that name drops. Unmissable if you finish the game.

The ending. "That just happened" pops as you finish Wheatley off - portalling to the surface of the Moon and letting the conversion gel and vacuum do the rest. This is the story-complete unlock: if you're here, you've beaten the single-player campaign.

Chapter 5, in the turret factory control room. Pull the master turret out of the template scanner (the one the factory copies every turret from) so the scanner reads empty, then step into the scanner yourself. You'll be sabotaging that template as part of the story anyway - just make sure it's you standing in the beam when it fires.

Clear every chamber in the Mass and Velocity co-op course (Course 2). Story-forced co-op progression - just work through it with your partner. This is also the course where Iron Grip and Triple Crown live, so consider knocking those out on the same run.

On the turret redemption line (also Chapter 5), one turret is flagged defective and sent off to be destroyed. Save it - grab it off the conveyor before it's crushed and set it aside. A small act of mercy, one pop.

Story-forced during the early escape. GLaDOS ushers you into a test chamber she's "helpfully solved for you already" - go in and complete it as she suggests. You can't progress without it, so it comes automatically. Taking her advice is the whole joke.

Land a cube on a button without ever picking it up yourself. The clean way: get the cube into an Excursion Funnel or drop it through a portal positioned directly above the button, so it falls straight onto it. Let physics do the placing - if you carry it there by hand, it doesn't count.

Perform 2 aerial gestures before you land, in co-op. Get airborne off a faith plate, a funnel or a big portal fling, then open the gesture wheel and fire off two taunts before your feet touch down. Any launch with a bit of hang time does it.

Clear every chamber in the Hard-Light Surfaces co-op course (Course 3). Story-forced. This is also home to Portal Conservation Society (finish Chamber 3 in only 5 total portals), so plan for that while you're here.

Break the rules in Test Chamber 07 by smuggling the Companion Cube out through the exit. Normally it's meant to stay behind - but before you leave, shoot a portal to grab the cube from beyond the door and carry it out of the chamber with you. Take the cube through the exit and this pops.

Perform all 8 gestures in co-op, of your own volition. Open the gesture wheel and work through every taunt at least once - wave, high-five, laugh, dance, the lot. Nothing stops you cycling through all eight back-to-back in the very first course, so just spin the wheel through each one. You unlock extra gestures by playing, so if you're short a couple, keep progressing and come back.

Clear every chamber in the Excursion Funnels co-op course (Course 4). Story-forced. Note Still Alive (finish this whole course with neither player dying) and Party of Three (the hidden companion cube) both live here, so a careful, no-death run through Course 4 can bag all three at once.

Complete every chamber in all five co-op courses - the full co-op campaign. Clearing Team Building, Mass and Velocity, Hard-Light Surfaces, Excursion Funnels and Mobility Gels gets you here. This is the co-op completion pop; if you've finished the campaign with a partner, it's automatic.

A single hidden portrait of Cave Johnson and Caroline. In old Aperture, after Enrichment Sphere 4 in Chapter 7, portal your way onto a panel beyond a closed gate and slip into the little office tucked behind it - the portrait's on the wall in there. Easy to stride straight past, so make the detour.

Discover the missing experiment - the Borealis. At the 1970s Aperture section (the very start of old Aperture, Chapter 6), climb up to the top catwalk and follow it round to a side room; hop on the furniture in the corner to reach a set of doors, and step outside to spot the ship sitting in dry dock. A lovely nod to Half-Life 2.

Dance in front of a turret that can't shoot you because a hard-light bridge is in the way. Put a bridge between yourself and an active turret so its shots are blocked, then bust out a gesture right in its face. Any co-op chamber that has both turrets and light bridges works - the Hard-Light Surfaces course is the obvious place.

Launch a turret off an Aerial Faith Plate (the spring-loaded jump pads). Find a chamber with a faith plate, carry or knock a turret onto it, and let it fling the turret across the room. Behold, flight. Any faith-plate chamber in the mid-to-late game works.

Win three rounds of co-op rock-paper-scissors in a row. It uses the RPS gesture and it's random, so the sane approach is to agree the outcomes with your partner up front - they deliberately throw the losing sign three times running. Trivial when co-ordinated, a coin-toss otherwise.

Taunt GLaDOS in front of a camera in each of the five co-op courses. Every course has GLaDOS cameras on the walls; stand in front of one and throw any gesture. You need one in all five courses - Team Building, Mass and Velocity, Hard-Light Surfaces, Excursion Funnels and Mobility Gels - so tick each off as you clear it, or you'll be trekking back for the one course you forgot.

Examine all the vitrified (shattered-glass) test chamber doors dotted through the mid-game. As you pass each ruined, sphere-etched door, walk up and look at it until the game registers it. There are several across the derelict chambers; slow down and inspect each rather than rushing on, and this ticks over once you've looked at the lot. Miss one and it's an easy chapter-select revisit.

After you've been refusing to co-operate, Wheatley sulks and eventually calls you back with an "Oh... you actually came back". Show that pit who's boss by walking straight to the edge and jumping in. You'll respawn fine - it's just you getting the last word. Follows on from You Made Your Point.

Chapter 8, Wheatley's very first test. Instead of solving it, just stand there and do nothing. After a while he gets flustered and the game moves on regardless - refusing to play ball is the whole achievement. Pairs naturally with Pit Boss.

Catch a cube painted with blue Repulsion Gel out of the air before it lands. Easiest to set up yourself: in a gel chamber, splash blue gel on the floor, drop a cube onto it so it bounces back up, and grab it mid-bounce before it touches down again. The chamber where you first mix gels is a good spot.

The last of the Rat Man's dens hides a radio playing a coded signal. In Chapter 2, Test Chamber 6, dig the radio out of the fallen rubble and - crucially - carry it with you through the Aerial Faith Plates into the hidden den. Bring the radio all the way in and it plays the hidden transmission (a picture encoded in SSTV tones). Don't put it down along the way or you'll have to fetch it again.

Enter 4 different portals without touching the ground, in co-op. Between the two of you there are four portal openings available (each player has their own pair), so set up a chain in an open chamber and fling yourself through four separate portals in one airborne run. Coordinate placements with your partner first - the Mobility Gels course, with its speed gel, makes building enough momentum easy.

Drop a portal directly under your co-op partner while they're mid-gesture. Get your partner to stand on a portalable floor and start a taunt (they're locked in the animation and can't move), then place a portal under their feet so they fall through. Easiest done by agreement. Named after Narbacular Drop, the student game that became Portal.

Drop your co-op partner into goo by pulling a hard-light bridge out from under them mid-gesture. Have your partner stand on a bridge you're projecting (over a pit of goo) and start a taunt; while they're locked in the animation, move the portal so the bridge vanishes and down they go. Best set up by mutual agreement, unless you enjoy betrayal. Pairs with Narbacular Drop.

You have to replay the co-op Calibration course, online, with a friend who has never played Portal 2 co-op before - that's the catch. Line someone up before they ever touch co-op; if all your mates have already played it, you're stuck waiting for a genuinely fresh partner. Play the whole Calibration course together and it pops for you. Sort this early - it's the single most awkward one to arrange late.

Chapter 3, Test Chamber 10 - solve the whole thing within 70 seconds of entering. Play it once normally to learn the route, then reload the chamber (chapter select or a save) and run it clean. 70 seconds is generous once you know the solution, so a practice run or two is all it takes.

Break 11 of Wheatley's monitors across Chapter 8. Once he's mugging at you through wall-mounted screens, destroy them - fling a cube from an Excursion Funnel, bat one with a turret, catch them with a laser, whatever the chamber hands you. There are exactly 11 breakable screens through the chapter; smash the lot. Keep an eye out in every room, as a couple are tucked out of the way.

Find the hidden Companion Cube tucked away in a co-op chamber. It's in the final area of the Excursion Funnels course (Course 4): shoot a portal at an out-of-the-way surface off to the left and ride the funnel across to reach the cube behind a set of opening doors. Go and give it a hug while you're there. Easy to grab on the same careful run as Still Alive.

Hug 3 different people from your Steam friends list during co-op. Perform the hug gesture next to a co-op partner who's on your friends list; you need three different friends, so it's usually spread across a few sessions. Needs willing mates who own the game - queue them up over a handful of co-op runs and hug each one.

Get through Chamber 6 of the Mass and Velocity course without ever losing a cube (letting one drop into the goo or a pit). Play it slowly and deliberately, agree with your partner who's carrying and placing what, and if a cube goes over the edge just restart the chamber and try again. See its sibling Talent Show in the Mobility Gels course.

Solve 3 chambers in the Mass and Velocity course each in under 60 seconds. Learn the solutions on a normal run first, then go back and blitz three of the quicker chambers one at a time - the timer is per-chamber, so you can pick them off individually rather than needing a flawless whole-course run. Same course as Iron Grip.

Complete Chamber 3 of the Hard-Light Surfaces course using only 5 total portal placements between the two of you. That's five portal shots for the whole chamber, combined - so work the solution out first and agree exactly who places which portal before anyone starts firing. Reset the chamber if you overshoot the count. The most planning-heavy of the co-op challenges.

Same idea as Iron Grip, but in Chamber 6 of the Mobility Gels course - complete it without losing a single cube. Slow and careful, co-ordinate who handles each cube, and reset the chamber if one ever goes over the edge.

Complete Course 4 (Excursion Funnels) without either you or your partner dying, once, the whole course. Deaths are cheap in co-op normally, so the only real trick is patience: take every chamber slowly and don't take risks near goo, lasers or pits. A single death by either player and you start the course over. Do it on the same careful run as Party of Three and Obstacle Building. A cheeky nod to the Portal 1 song.