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    The One Free Bullet Achievement Guide by Thundaka

    Version: 1.00 | Updated: 11/11/12 | Printable Version | Search Guide | Bookmark Guide

                                   HALF-LIFE 2: EPISODE ONE
                            ďTHE ONE FREE BULLETĒ ACHIEVEMENT FAQ
                               By Thundaka (thundaka@yahoo.com)
    Copyright 2012 Thundaka.
    This guide is solely for private use.  If you wish to host this guide on your
    website, contact me for permission before doing so.  Any profitable use is
    strictly prohibited.
                                    VERSION HISTORY
    v1.00: First version.  Feel free to e-mail me with any questions or 
    Welcome, brave player, to ďThe One Free BulletĒ achievement guide.  This is 
    arguably the most difficult achievement in the entire Half-Life series, as it 
    fundamentally alters the way the entire game is played.
    Put simply, this achievement requires you to give up your guns for an entire 
    playthrough.  With the exception of the titular bullet (to shoot open a lock 
    at the start of Chapter 3), you must rely on your crowbar, explosives, and 
    especially the Gravity Gun to get Gordon Freeman safely out of City 17.  
    While the opening and closing battles arenít particularly terrible, the 
    middle chapters make for some of the most taxing battles in the series.  
    Effective use of the environment, good reflexes, and thorough preparation are 
    all important to your survival.
    With that in mind, I urge anyone pursuing this achievement to REDUCE THE 
    DIFFICULTY TO EASY.  Gordon loses health and Suit Power at an alarming rate 
    even on the lowest setting, due to his cumbersome ďammunitionĒ and reliance 
    on explosives, but the greatest danger is Alyx.  Her regenerating health 
    makes her essentially invulnerable on Easy, but at the higher difficulties 
    she can quickly get overwhelmed and killed by mobs of Antlions or Zombines--
    and with explosive barrels and the like as your main weapons (especially 
    during the infamous elevator battle), Gordon canít do a lot to prevent it.  
    Every achievement can be earned at any difficulty, so donít make things 
    more difficult than they already are.
    --GRAVITY GUN: I hope you love the Zero-Point Energy Field Manipulator, 
    because for most of the game it is the only weapon available.  The burst 
    from the primary trigger can directly damage Headcrabs, killing them in 
    three hits if no physics objects are available.  It can also flip over 
    Antlions--a valuable ability when they attempt to mob you--though they do 
    not take damage.  Against larger enemies, the Gravity Gun is only as good 
    as the objects it can throw at them.  Your battle strategy is heavily 
    dependent on the objects scattered throughout each arena, and so those 
    objects deserve a more detailed discussion.
    Gun is that it can turn nearly anything in the environment into a projectile.
    Not every object is made equal, though.  Small objects like rocks can kill 
    a Headcrab or finish a common Zombie with a well-aimed headshot, but do 
    little damage to tougher enemies and are worthless in a mob situation.  
    Heavier objects have much more stopping power, but their bulk often obscures 
    your vision and makes aiming difficult.  (On the flip side, this same factor 
    makes them decent shields against gunfire.)  In all cases ricochets are a 
    major issue; even a successful kill will send the object bouncing in a 
    random direction, forcing you to run after it and aim at your next target 
    while the other enemies are free to attack you.  You will spend as much time 
    running as you do attacking, so conserving your energy for a well-timed dash 
    is a constant tactical consideration.
    	*OIL DRUMS: The rusted metal barrels found throughout Chapters 3 and 4.
    Since they are both common and do good damage, they are one of the best 
    weapons for a big portion of the game.
    	*EXPLOSIVE BARRELS: These red-and-white barrels explode on impact, 
    heavily damaging every enemy within a wide radius, and are great for thinning 
    out a crowd.  Unfortunately, playing with explosives can be dangerous: the 
    blast will ignite any nearby barrels (sometimes launching them at you just 
    before they detonate), a charging enemy can catch you in the blast, and a few 
    stray bullets or a Zombineís grenade could lead to premature detonation.  
    While they are too powerful to ignore, you must handle these weapons with 
    	*GAS TANKS: Orange canisters that detonate on impact like the explosive 
    barrels, and also light any survivors on fire.  Many of the barrelsí problems 
    apply here, though the smaller blast radius and lower damage do lower the risk.
    	*FLARES: These glowsticks are valuable for setting zombies on fire, 
    which also helps save the flashlight battery, and--if the player is fast and 
    accurate--can be reused to kill two or three per flare.  Earning the 
    Zombie-que achievement (see below) is heavily dependent on such reuse.  The 
    catch is that flares have a severe time limit: the moment one is picked up, 
    you have a limited time to toss it before it burns out.
    	*HOPPER MINES: Probably the best ďammunitionĒ the Gravity Gun gets.  If 
    picked up and thrown, they serve as powerful explosives which cannot 
    prematurely detonate.  If set back down, they can form a perimeter that 
    eliminates your enemies while you stay at a safe distance.
    --GRENADES: These explosives are very powerful in mob situations or tight 
    corridors, but due to limited numbers you need to be very careful how you use 
    them.  (Sadly there are no infinite Grenade crates in this game.)  The 
    location of each grenade will be noted in the walkthrough, as well as the 
    best battles in which to use them.
    --CROWBAR: While still useful, Gordonís trusty melee weapon will see little 
    action.  It arrives late in the game, about the same time you earn the rocket 
    launcher, so the rest of your arsenal renders it mostly obsolete.  It is still 
    needed for one hit kills vs. headcrabs and barnacles, but donít expect much use 
    beyond that.
    --ROCKET LAUNCHER: This weapon single-handedly makes the game a dozen times 
    easier.  The rocket launcher provides both range and high damage, allowing 
    you to kill clusters of enemies well before they can reach you, and thanks to 
    the numerous infinite rocket crates your ammo is rarely a concern.  Add in 
    that two of the gameís three bosses are only vulnerable to rockets, and this 
    weapon stands head and shoulders over all others.
    The observant player will note that this achievement relies heavily on thrown 
    explosives and physics objects, a playstyle that meshes well with the 
    ďZombie-queĒ achievement.  Since there are only 13 flares in the game, and 
    you are required to light 15 zombies on fire, reuse of your flares is 
    mandatory.  This guide will point out the location of every flare in the 
    game, as well as tactical advice to get the most mileage out of each one.  
    As a rule of thumb, the slow-moving common zombies and Poison Zombies make 
    the best targets.
    Keep in mind that only living zombies count toward the total (headcrabs and 
    corpses do not), and that gas tanks and other flammables do not count.  All 
    but two of the flares appear in Chapter 3, so plan accordingly.
    Little needs to be said about the first two chapters.  The supercharged 
    Gravity Gun turns every battle into a cakewalk, and with no other weapons 
    your playstyle is unchanged.
    The only object of note in this section is the Suit Power station at the 
    start of Chapter 2, just before Alyx sends you down the elevator into the 
    Core.  Do not use that station when you first arrive.  Wait until the Core is 
    stablized and drains your HEV Suit Power, and you can enter the third chapter 
    with 30 Suit Power instead of zero.  Do your best to avoid taking damage from 
    the roller mines by the train station, and you should be in decent shape when 
    you exit the Citadel and enter the difficult part of the game.
    *Part 1: A Walk in the Dark*
    -Flares: 5
    -Batteries: 5
    After catching your breath, you will head into a hallway littered with 
    zombies, headcrabs, and Hopper Mines.  Alyx can finish most of them by 
    herself, though there are plenty of oil drums and rocks for you to throw.  
    Clear out any unexploded Hoppers, enter the pitch-black tunnel, and collect 
    the BATTERY next to the vent on the floor.  You will need the flashlight to 
    guide you through the vents and into the next room, though you can save the 
    battery by grabbing the first FLARE across a gap with the Gravity Gun.  This 
    one wonít last long enough to burn any zombies, so just use it for light.
    Pretty soon you will drop into the next room, crushing a headcrab in the 
    process.  To proceed you must grab the pistol inside the cage, by gripping it 
    with the Gravity Gun and lifting it through the gap.  Gordonís one bullet is 
    used here, to break the lock on the door between yourself and the fuse box.  
    It should go without saying, but DO NOT MISS this shot.  Flip the fuse box to 
    open both doors, then blast the car to open the way forward.  There are four 
    BATTERIES in this room, plus a second FLARE in the gun cage.  If you save the 
    flare until the path is cleared, you can light up your first two zombies for 
    Shine your flashlight on the enemies to help Alyx gun them down.  Remember 
    that you can flip the antlions with a Gravity Gun burst, making them easier 
    targets and stopping their attacks.  There is a BATTERY next to a dead rebel 
    left of the entrance, a little health in the car before you pass through the 
    rubble, and two gas tanks on the path.  Up ahead is a lit train car, 
    containing the first of the hateful Zombines.  They are a lot tougher than 
    common zombies (it takes a direct hit from an explosive barrel or two from 
    an oil drum to kill them), and they run fast and hit hard, but they are at 
    their worst when they pull out a grenade for their suicide rush.  I 
    recommend dashing back into the train and letting Alyx deal with them, 
    either gunning them down or triggering the suicide attack while you are at 
    a safe distance.  There are three explosive barrels which can be tossed at 
    them, plus a third FLARE (inside a van at the very end of the tunnel) with 
    which you can burn one or two Zombines, but I donít recommend it: your 
    accuracy is very poor in the darkness, and the combination of rushing 
    enemies and grenades make the barrels very dangerous.
    You will meet your first Barnacle on the path ahead.  With no crowbar and 
    no guns, you will die if it catches you; shine your flashlight to have Alyx 
    kill it, and avoid the tongue at all costs.  To open the door to the next 
    area, activate the fuse box in the alcove just beyond.  There are two more 
    FLARES, one outside the alcove and another next to the door, which you can 
    use to light up the four zombies that arrive once the power is switched on.
    *Part 2: Antlion Wrangling*
    -Grenades: 1
    -Batteries: 3
    -Med Kits: 5
    Up the stairs is a pack of three slow but deadly Poison Headcrabs.  You can 
    kill them directly with a few Gravity Gun bursts, though it is safer to 
    grab an oil drum and toss it for an instant kill.  There is a MED KIT at 
    the top of the stairs, a BATTERY in the corner with the generator, and 
    another BATTERY inside a locker to your right.  You wonít go far before 
    discovering the first antlion burrow.  Push the nearby car over the burrow 
    to seal it.  If this doesnít kill the antlion outright, a burst from the 
    Gravity Gun and a few bullets from Alyx will do the job.  Two more Poison 
    Headcrabs will enter while you raise the gate.  Exterminate them, then 
    finish raising the gate and continue ahead.
    The area ahead holds a long, dark tunnel that is infested with Barnacles.  
    Shine your light straight up to kill the nearest ones, but leave the rest 
    alive.  Two waves of zombies will approach once you enter the tunnel.  The 
    Barnacles at the far end will grab them one by one, killing them long before 
    they can reach you.  Once all the zombies are eliminated, have Alyx finish 
    the Barnacles.  (Again, avoid their tongues at all costs.)  Three more 
    Zombines will attack when you reach the end of the tunnel.  The Alyx-
    centered strategy from earlier works well, though if any of them focus on 
    you it will be necessary to start running.  There are plenty of oil drums 
    around, so be sure to toss them to help eliminate the Zombines.  There is a 
    final Zombine in the dark corner near the doors, though you can eliminate 
    it by tossing an explosive barrel from a distance.  Donít forget to grab a 
    MED KIT from the antlion burrow before continuing on.
    The three-story parking lot ahead is the first really nasty section of the 
    game, and a good reminder of why Easy mode is recommended.  Some Zombines 
    and antlions are fighting when you arrive, though pretty soon both parties 
    will notice you and come charging down the hall.  Stay behind Alyx while 
    the Zombines attack, and flip over the antlions to help her finish them.  
    Once inside the lot all three burrows will erupt with antlions, and you 
    will need to block all three with cars to proceed.  Only one car is 
    available at first; sprint toward it, then push it until it covers the 
    most distant burrow (directly below the second level).  While you can 
    knock back some antlions with the Gravity Gun, donít expect to do this 
    without taking a few hits.  Once the burrow is sealed, you must sprint 
    up the ramp to the second level.  Inside the alcove straight ahead is the 
    first and only GRENADE in this chapter.  Do not miss it, or you will 
    suffer later.  Punt the second car down to the lower level, and seal off 
    the nearby second burrow.
    Only one car remains, but it is a nasty one.  You must travel to the 
    upper level, then drop into the closed-off parking space with a Zombine.  
    With no objects to toss and no support from Alyx, you have no choice but 
    to stand on the car and wait for its suicide attack, then crouch behind 
    the car to reduce the damage.  (Thankfully there is a MED KIT to help you 
    recover.)  Open the gate, push the car down to the ground floor, and seal 
    the final burrow.  Once you and Alyx have killed the final antlion, you 
    can open the gate on the third floor and finally claim the BATTERY and 
    two MED KITS up there.  I suggest taking a breather, because it only gets 
    more intense from here.
    *Part 3: Hellís Elevator*
    -Flares: 6
    -Batteries: 4
    -Med Kits: 9
    Descend the stairs into a fenced-off sewer area.  There is no safe way to 
    use the explosive barrels, so rely on oil drums for your damage.  One 
    Zombine will charge at you near the beginning, then a few more when you 
    reach the second room.  The narrow quarters make the Zombines easy to hit, 
    but also make the suicide charge very dangerous.  I suggest doubling back 
    after entering the middle area (which will draw out the Zombines near the 
    far door), and dashing back up the stairs if any of them pull out a 
    grenade.  A final group will pursue you as you exit, but you have plenty 
    of time to run ahead and shut the door behind you.
    Up the stairs is a large arena, containing the elevator that will finally 
    carry you to the surface.  However, to ride it you must survive one of the 
    toughest brawls in Half-Life history.  Since the objects in the environment 
    are so important, a quick survey is in order:
    -FLARES: In the corner near the entrance, 2 next to the elevator itself, on 
    the path to the fuse box (on the left next to an explosive barrel), in the 
    second cage on the path, and inside the fuse room.  You can easily earn 
    Zombie-que here if you use all of them--there will be no shortage of 
    targets to burn, and often they crowd closely enough to ignite 2 or 3 with 
    a single toss.  Just be aware that the first and last flares require major 
    detours, while the one in the cage needs to be used on the way to the fuse 
    room (you wonít have time to pull it out of the cage when they arrive en 
    -GAS TANKS: In the corner near the entrance, 2 next to the elevator, 2 
    behind the cage next to the elevator, and in the dead-end room a bit 
    beyond that.  They are great weapons, but keep them spaced out; they 
    really hurt if the Zombines detonate them, especially if explosive barrels 
    are nearby.
    -EXPLOSIVE BARRELS: On the path toward the fuse box, and at the corner 
    where the two paths meet.  Keep them far from each other, and from the gas 
    -OIL DRUMS: Right next to the explosive barrels.
    -BATTERIES: Next to the elevator, in the first cage on the way to the fuse 
    room, outside the fuse room, and in a corner room past the fuse room.  Be 
    careful with the last one: that room holds a Zombine and lots of 
    explosives, killing or seriously hurting you unless you can dash away fast 
    -MED KITS: In the corner room past the elevator, 2 on the path to the fuse 
    box, in the first cage, 2 in the second cage, 2 inside the fuse shed, and 
    in the explosive-filled corner room.  Itís a good idea to toss them toward 
    the elevator, because you will really need them once the fight starts.
    While they donít attack in force until the power is on, the zombies will 
    still arrive one or two at a time on the path to the fuse shed.  You 
    cannot fight back without the flashlight, so keep a close eye on the 
    suitís battery power.  (The flares provide some illumination, but not 
    enough to see the zombies coming from a distance.)  I suggest switching it 
    off at the halfway mark, then waiting for the power to recharge--unless you 
    hear a zombie coming, in which case you must keep it on until the beast is 
    dead.  You will need to dash a lot to survive the Zombines, so conservation 
    is critical.
    Let your batteries recharge before opening the fuse shed, as a Zombine will 
    come charging out with a grenade.  Exterminate the headcrab that waits 
    inside, and you can turn on the power.  The zombie hordes will arrive on 
    the way back to the elevator.  The epic brawl that follows boils down to 
    battery management, which you will badly need for light and to dash away 
    from the Zombines and especially the Fast Zombies.  Both the gas tanks and 
    flares provide light to see by (in a pretty small range), but they are 
    limited, and you need to refrain from dashing as well in order to recover 
    your flashlight power.  While the explosive barrels and gas tanks are most 
    powerful, the oil drums are the most reliable projectiles: they are 
    infinitely reusable and cannot damage you, and the only easy way to kill 
    Fast Zombies (though you will need to chase after the barrel each time it 
    is thrown).  No matter what you are using, remember to DROP THE OBJECT and 
    run when a Zombine pulls out a grenade.  You canít dash while using the 
    Gravity Gun, and even on Easy mode this does a ton of damage at close range.
    When Alyx finally announces that the elevator has arrived, hurry in ASAP.  
    The hard part is by no means over, but at least the very worst is behind you.
    *Part 1: Return of the Combine*
    -Batteries: 2
    -Med Kits: 4
    Once you have recovered, hunt in the side room for the crank that opens the 
    gate to the surface.  There is a MED KIT and BATTERY in here as well, both 
    surely welcome after the beating you took.  Take a look around, listen to 
    Dr. Kleiner, and stretch your legs a bit before you tackle the next combat 
    section.  Some observation drones will appear up ahead, which you can grab 
    and smash for an additional battery or two.
    Keep the Grenade in hand as you walk forward.  Four Combine soldiers will 
    rappel down from the roofs, then start firing at you.  They take and deal a 
    lot of damage, and the only nearby object (a trash can) is too light to 
    even make them flinch.  However, a perfectly thrown grenade can kill several 
    of them as they touch down.  To deal with the survivors, I suggest doubling 
    back and grabbing one of the metal panels that blocked your path earlier.  
    They are heavy enough to kill a soldier in one toss, though the wild 
    ricochets make them difficult to use more than once.  Odds are Alyx will do 
    most of the damage.
    When the soldiers are cleared you can move into the street ahead, where a 
    few Combine and a whole mess of antlions duke it out.  There are several 
    MED KITS in the starting area, if you need it.  Hang back until the antlions 
    finish off the soldiers, then start sealing up the burrows with cars.  A few 
    more Combine wait behind the door at the streetís end, ready to ambush you, 
    but the trap to the left of the door provides an easy way to clear them.  
    Grabbing the nearby chair with the Gravity Gun should trigger the traps, and 
    if you back up quickly you wonít be hurt.  The downside is that a raging 
    fire blocks the way forward, forcing you to solve a platforming puzzle before 
    you can continue.  Collect the BATTERY in this room, then take the stairs.
    *Part 2: Headshots*
    -Grenades: 8
    -Batteries: 8
    -Med Kits: 4
    The zombies on the top floor are not a concern, as the traps and roller 
    mine make quick work of them.  Catch it with the Gravity Gun once they are 
    dead, and Alyx will turn it to your side.  Grab the MED KIT and BATTERY up 
    The sniper outside will make your life difficult, so proceed with caution.  
    The hacked roller mine can hold off the still-hostile one in the street, 
    but pretty soon you will have to grab that one and hack it as well.  Make a 
    mad dash to the wall on the right, dodging fire from the soldier at the 
    mounted gun as well as the sniper.  To take out the sniper youíll first 
    need to get behind the second car in the street, hiding behind cover to get 
    there.  Rather than wasting a Grenade, grab one of the roller mines and toss 
    it into the sniperís nest to take him out.  Toss the other at the Combine on 
    the ground, then stand back until they explode and Alyx takes the sniper 
    rifle.  Donít forget to grab the three GRENADES behind the mounted gun and 
    the MED KIT behind the car.
    The area ahead is infested with zombies, but thanks to Alyx and her 
    impeccable aim you can focus on avoiding damage while she eliminates them.  
    Climb over the fence and draw them out of their hiding place in the alley.  
    The common zombies arenít much threat, so focus on keeping your distance 
    from the Zombines and Fast Zombies.  Head inside the building, and up the 
    stairs you will find a boarded-up set of windows that looks down on the 
    street below.  Knock out these boards to expose this corridor to Alyx, 
    allowing her to pick off the zombies that come shambling down it.  She 
    probably wonít take out the Zombine that runs after you, so just try to 
    stay out of reach until it commits suicide.  Past this area you will find 
    two more GRENADES and three BATTERIES in crates.
    Antlions spawn in the street ahead, though the Combine cut them down from 
    two different directions.  First you will need to eliminate the Combine 
    who covers the path ahead, by taking the back panel to give Alyx a clear 
    shot.  Next on the list is the antlion burrow, which must once again be 
    sealed with a car.  That just leaves the Combine at the end of the street, 
    who keep the gate shut except to rush out three at a time.  Alyx can make 
    short work of them, but until you sneak past the gate they will keep 
    respawning.  The panel from the mounted-gun Combine works well as both a 
    shield and a heavy projectile, so carry it with you as you approach the 
    gate.  When the Combine are gone Alyx will come to you, followed by a few 
    antlions; flip them over as usual to help her finish them.
    Pick up the MED KIT right after the loading screen.  The building ahead 
    has lots of tight corridors with plenty of Combine, making Grenades 
    especially powerful.  You probably have five of them already, so feel 
    free to use them all to thin their numbers.  There is another GRENADE 
    in the side hall next to the first cluster of them, and another 2 GRENADES 
    by the sealed-off doors.  Those doors donít stay sealed for long, though, 
    so start tossing Grenades as soon as they explode to take down the strike 
    force.  This room contains a Suit Power recharge station--the only one in 
    the game outside the Citadel--as well as a Health Station and two 
    BATTERIES, so fill up.  Grab the radiator on the wall up ahead.  It is 
    remarkably damaging for such a small object, and the perfect way to take 
    out the final shotgun-wielding Combine up ahead.  At the top of the stairs 
    are two MED KITS and two BATTERIES.  Your health and Suit Power are 
    probably full, so drop them into the garage to help you recover after the 
    next fight.
    *Part 3: Boom!*
    -Grenades: 4
    -Batteries: 5
    -Med Kits: 10
    You will drop into the gameís first boss battle, a brawl between the 
    Combine and an Antlion Guard which quickly becomes you vs. the Guard and 
    its antlion allies.  There are seven explosive barrels and several more 
    oil drums around the arena, though safely using them can be difficult.
    Make a mad dash for the explosive barrel in the upper-left corner, and 
    you can hit the Guard while itís still attacking the Combine tank.  With 
    any luck you can grab and throw a second barrel before the Guard has 
    finished the Combine and turned its attention toward you.  It only takes 
    one more explosive barrel (or two solid tosses from an oil drum) to finish 
    the Guard, but tossing it while the Guard is galloping toward you and its 
    brothers try to mob you is no simple feat.  Whenever possible, try to trick 
    it into running into the walls; this will stun it for a few seconds, giving 
    you time to recover your suit battery and move far enough to safely toss an 
    explosive barrel.
    When the Guard dies Alyx will hop down to join you, providing cover fire 
    while you seal the three antlion burrows.  After that you can recover your 
    health (and Suit Power, if you remembered to drop the batteries), before 
    more drones arrive and the Combine start shooting from the rooftops.  You 
    have nothing to contribute here, so just stay in a corner while Alyx 
    eliminates them with the mounted gun.  A few more Combine are sitting in 
    the trench just ahead; you could carry an explosive barrel over or toss a 
    Grenade to try and eliminate them, but Alyx and the rebel on the roof 
    will probably do most of the damage.  Be sure to pick up the GRENADE in 
    the trench, which you will need up ahead.
    The next few rooms are light on combat, but full of deadly explosives 
    which make navigation difficult.  Pull out the Hopper Mine by the door 
    and climb into the vent, taking the ladder up the side path and collecting 
    two BATTERIES with the Gravity Gun.  Go far enough and the vent will 
    collapse, trapping you in a room criss-crossed with tripmines and 
    explosive barrels.  At that point you would need to carefully maneuver 
    to the exit, jumping on top of barrels and praying that you donít tip 
    them over while you cross.  However, you can eliminate the danger by 
    tossing a Grenade out the end of the vent, detonating all the explosives 
    and letting you walk straight to the elevator.  In typical Half-Life 
    tradition, once you enter the elevator will plunge into the water below.  
    Knock out the roof escape with the Gravity Gun, then climb onto the ledge 
    with the MED KIT.  This room is very hard to navigate while the 
    explosives are there, but by grabbing and tossing an explosive barrel you 
    can eliminate them at no risk.  Watch out for the Barnacles on the 
    ceiling.  They take some time to extend their tongues and can be 
    distracted by the explosion debris, but if you are caught you will 
    absolutely die.
    Kill the Poison Headcrab inside the lower room, collect the two MED KITS, 
    and crawl through the vent to the upper level.  Hop around the outside of 
    the shaft, taking care to avoid the Barnacles, and you can climb a ladder 
    all the way to the vent near the top.  A Barnacle stands between you and 
    the final jump to the vent, though you can pull the vent cover toward you 
    to keep the tongue occupied.  A final booby-trapped room waits at the end 
    of the vent, so gently drop the vent cover into the room below to clear 
    the way.  Watch out for the Hopper Mines, which are still standing and 
    must be pulled out one at a time.  Activate the fuse box to open the door 
    forward, and grab a Hopper before heading to the next area.  (You could 
    bring all four Hoppers to add to your ammo stockpile, though honestly itís 
    not worth the six extra trips back and forth across the loading screen.)
    Set down the Hopper, then peek forward into the room ahead.  A zombie will 
    come crawling toward you, which Alyx will quickly kill if you move out of 
    her way.  Rather than exploding everything now, you should carefully move 
    the explosive barrels out of the room and back through the corridor.  This 
    will allow you to set off the tripmines without wasting projectiles that 
    you can use against the Combine.  Remember to pull out the Hopper Mine, 
    which could easily cause a fatal chain explosion.  Once the room is clear, 
    collect a BATTERY and health from the locker and two GRENADES from a 
    supply crate; you can bring back the explosive barrels as well, provided 
    that you keep them near the locker.  A Combine assault team enters after 
    you approach the sealed-off exit, exploding the door and dropping a 
    burning barrel before they enter in force.  It only takes two good 
    explosions to eliminate them, so fire away.  After they are dead you can 
    pick up another BATTERY from the stairs, then pull the plug to remove 
    the force field.
    There is one more Combine battle before the game gives you a break.  
    Unfortunately itís a hard one, as it takes place in a wide-open street 
    that gives the Combine a huge range advantage and enough room to dodge 
    your projectiles.  Before facing them head-on, move the enemy Hopper to 
    the bottom of the stairs and lure in the Combine to thin their ranks.  
    You shouldnít set more than one Hopper at a time (they will all explode 
    when a soldier approaches, even from the other side of the wall), but 
    you can hold a second Hopper and drop it in the same spot when the first 
    one explodes.  You probably wonít kill them all, but finishing two or 
    three this way can really curb the damage you will suffer.  Once in the 
    street you should focus on clearing the distance to the soldiers; 
    Grenades and oil drums are your best weapons (and the latter is helpful 
    as a shield), though once again Alyx tends to do more damage.  The 
    Combine do throw Grenades of their own, which can be thrown back if 
    youíre quick enough with the Gravity Gun.
    Things get a lot easier after you pass the first car, when a rocket-
    firing Resistance member joins the fight.  You can afford to hang back 
    a bit here: his rockets will quickly blow away the Combine, and if they 
    do kill him Gordon will gain the godly ROCKET LAUNCHER a bit early 
    (plus three free rockets, which can be a huge help on the path to the 
    hospital).  A big group of them will blow open a door at the end, so 
    you might want to prime a Grenade (or collect the explosive barrel by 
    the exit) and toss it at them after the explosion.  The action lets up 
    for a bit, giving you the opportunity to catch your breath and collect 
    the two MED KITS in the street.  Donít forget to collect the BATTERY 
    in plain view and the GRENADE in a supply crate before entering the 
    apartment complex.
    *Part 4: The Rocket Doctor*
    -Grenades: 3
    -Batteries: 10
    -Med Kits: 11
    After hanging out with the Resistance for a bit, pick up the MED KIT 
    behind the marked door and head up the stairs.  The first door is 
    blocked, while the second has two Zombines who will charge once it is 
    opened.  Try to roll in a grenade before Alyx fires, then close the 
    door again; this can take out one of them right away, making it much 
    easier for Alyx to finish the other.  As before, backpedal down the 
    stairs if they use the suicide attack.  There are no good projectiles 
    around, so youíll need her to finish the next Zombine as well.  Stick 
    to the left in the next room, or youíll be sorry: the floor will 
    collapse, dropping you into a room full of zombies.  You can take them 
    out pretty quickly by tossing furniture, but the Zombine in the hall 
    outside is very difficult to kill and almost impossible to slip past.  
    The top floor has a BATTERY and two MED KITS, while the room below 
    only has MED KITS.
    Upstairs you meet Barney, who reunites you with another old friend: 
    the CROWBAR!  This isnít as exciting a reunion as you might hope, 
    since itís so late in the game, but itís still pretty helpful: 
    Barnacles are no longer a death sentence, and headcrabs will go down 
    in one hit.  Straight ahead are a BATTERY and MED KIT, guarded by a 
    headcrab.  Up the stairs are some Poison Headcrabs, whose slow 
    reflexes make them easy crowbar targets.  Pick up the GRENADE in a 
    supply crate, lure the two Zombines to you, and then back up while 
    Alyx kills them.  (The crowbarís damage is too low, and in any case 
    fighting them in such an enclosed space is a very bad idea.)  After 
    that, head outside and smash the board blocking the bridge to draw 
    the Combine toward you.  I recommend Grenades for the two who cross 
    the bridge, and the explosive barrel to take out the one on the 
    roof.  Spend as little time as possible in the open, since the 
    gunship is still on the prowl.
    Cross the bridge to enter the next indoor area, a long hallway 
    crowded with zombies, tripmines, and eventually a squad of Combine.
    The gunship shoots at you through the windows, so make a point of 
    staying low and near the wall the whole time.  The crowbar is pretty 
    useful against the common zombies (if you have good reflexes and 
    can pull back quickly), but for the Zombines youíll still want to 
    rely on the Gravity Gun, Combine traps, and maybe Grenades.  Since 
    the Combine will be firing at them the whole time, itís a good idea 
    to hang back until the zombies are dead.  Use any remaining Grenades 
    to eliminate the Combine; if you already have the rocket launcher, 
    this is the ideal place to use it.  There is a MED KIT in a locker 
    near the beginning of the hall, and a GRENADE in a crate at the end.
    The gunship finally catches up to you up ahead, setting the stage 
    for the second boss fight.  The ROCKET LAUNCHER is downstairs next 
    to a Resistance corpse; you will need it to win the battle.  On Easy 
    mode it takes three rockets to kill the gunship.  While you could 
    theoretically do this without reloading, in practice the 
    gunshipís defenses and the bits of building in the way will probably 
    cause several to miss.  The key to this battle is reaching the 
    infinite rocket crate in the center without leaving yourself totally 
    exposed.  My strategy is to hang out near the entrance, dodging 
    behind the left wall while it fires, then sprint out to fire a rocket 
    right after.  You canít just stand there and fire, as its guns cut 
    through your Suit Power and health very quickly even on Easy mode.  
    (There are 4 MED KITS downstairs to help with the latter, but no 
    batteries.)  Remember to fire the rockets in a spiral path, to 
    outmaneuver its anti-missile guns and close in on the gunship for 
    the kill.
    After three rockets you must sprint back to the crate, quickly but 
    carefully: the path to the crate is narrow and has a sharp turn, and 
    itís easy to fall down and be forced to repeat the journey.  Once 
    there you should hop downstairs (the floor above makes decent cover), 
    then sprint up the stairs and back to the entrance.  Throughout the 
    battle pieces of the building will break off as the gunship and your 
    rockets hit them, rapidly destroying cover and making both of you 
    easier targets.  You could spend a round destroying the roof in order 
    to clear your field of view, though since the most inconvenient bits 
    are quickly destroyed anyway I wouldnít bother.
    Reload on rockets when it dies, then pick up any Med Kits you missed.  
    Some clueless Combine will blow the door, only to be blasted to 
    smithereens by your rockets.  Pick up the GRENADE near their bodies, 
    use the Gravity Gun to set off the tripmines down the hall, pull out 
    the Hopper Mine hidden in the corner, and pick up two BATTERIES from 
    the locker.
    The next section is perhaps the most satisfying part of the 
    challenge, and certainly the easiest.  You will walk through a 
    Combine- and zombie-infested hospital, with an infinite supply of 
    ammo for Gordonís instant-kill weapon.  It may be a long walk in 
    places, but there is not a single loading screen between Gordon and 
    the crate during this section.  Better still, Alyxís new shotgun can 
    kill most enemies in one or two shots, and there are lots of Hopper 
    Mines for even more instant kills.  While you should always use the 
    nearby explosives first and let the two sides kill each other before 
    intervening, there is no need to hoard your resources like you have 
    for most of the game.
    The first side room to your left has a BATTERY, though you will need 
    to escape the zombie that hides in the bathroom.  There are more 
    BATTERIES around the bend (in the first room on the right), at the end 
    of the same hallway (behind the door which a zombie breaks down), and 
    inside the operating room that links to the third hallway.  The Combine 
    Elites and their energy balls make their debut in the next hall, though 
    more often than not they will die before they ever get the chance to 
    attack you.  The fourth and final hallway has two more BATTERIES, one in 
    plain sight and another in the TV room with two zombies.  Take them out 
    with the Gravity Gun, then open the door holding back the zombie crowd 
    and get ready to back away.  These guys are pretty tough--especially the 
    Poison Zombie, who can survive a direct rocket hit--so donít be surprised 
    if takes all three rockets and even a grenade or two to finish them.  
    Make sure that the rocket launcher is full before you jump down, as you 
    canít return to the crate after this.
    *Part 5: Emergency Checkout*
    -Flares: 2
    -Batteries: 7
    -Med Kits: 1
    The floor collapses below Gordon, dropping him into the flooded basement.  
    before she arrives, the gameís programming gets screwed up and she will 
    not rejoin you upstairs.  (She will reappear at the next loading screen 
    when Chapter 5 starts, but there are two tough battles in the meantime 
    which become much tougher without her help.)  After she says her piece you 
    can swim down, then move up onto the ledge.  There is a Poison Headcrab in 
    the shed; kill it with the crowbar, then collect the two BATTERIES.  
    There are another two BATTERIES next to the door, which you must power up 
    before exiting.
    Keep the crowbar handy in the water, as there are lots of Barnacles for 
    you to kill.  There is one by the alcove with the floating canister, one 
    by the platform near the electric switch, and two near the stairs, all 
    of which must die right away.  There are two more near the shed, but you 
    cannot reach them yet.  Move the canister under the platform next to the 
    switch, so you donít electrocute yourself in the water, then turn on the 
    power.  From here it takes two careful jumps to reach the ledge adjacent 
    to the shed--at which point the final two Barnacles arrive, blocking your 
    path with their tongues.  Carefully backtrack to the switch, turn it off, 
    and you can safely kill them with your crowbar.  From there you only need 
    to reactivate the power, tread the same path, and this time jump to the 
    shed and through the window to safely reach the door.
    Upstairs Alyx will join you, having ditched the shotgun and returned to 
    her automatic pistol.  Not too far ahead is another zombie fight, this 
    time in an enclosed arena just below you.  Two Fast Headcrabs are running 
    around on the floor; either wait for Alyx to finish them, or just jump 
    down with the crowbar and take the damage.  The final two FLARES are down 
    here on the shelves.  If youíre not worried about ďZombie-que,Ē use one 
    to burn the tough Poison Zombie to death.  Otherwise you should dodge the 
    Poison Headcrabs as he throws them (they are much easier to kill after 
    they detach from his body) and kill him with the crowbar once itís just 
    him.  The same goes for the Poison Zombie outside the broken window, 
    which is harmless once his headcrabs are gone.  Pretty soon a crowd of 
    zombies will start banging on the doors.  Set a Hopper Mine near both 
    doors, and pick up the third as ammunition.  It will take all three 
    rockets and possibly some grenades to thin out the horde, though they 
    are clustered tightly enough that you can easily light two or three at 
    a time with a single tossed flare.  Concentrate on killing the Zombines 
    first, and with luck you should escape with only minor damage.  Pick up 
    the two BATTERIES after the battle, then continue on.
    There is a MED KIT and a BATTERY in the next operating room.  There is 
    one more obstacle before you leave the hospital, a hallway that is 
    scattered with Hopper Mines and guarded by two turrets.  Pull the first 
    Hopper before you continue, then move down a little to trigger a wave of 
    zombies, including some Zombines and a scary Fast Zombie.  Dash out of 
    the hall and close the doors behind you, and hopefully Alyx and the 
    turrets will finish the zombies before they can reach you.  Some more 
    zombies arrive as you enter the first door on your left, though if you 
    hide Alyx and the turrets should take out all of them.  Sprint to the 
    room on the opposite side, pulling out any Hoppers which didnít already 
    detonate, and you are nearly home.  Now you only need to remove the 
    Hoppers just behind the force field, pull the plug that powers the 
    force field, and run on to finally leave the building and get a taste 
    of fresh air.
    --CHAPTER 5: EXIT 17ó
    *Part 1: The Battle of the Trainyard*
    -Grenades: 2
    -Batteries: 1
    -Med Kits: 3
    Pick up the BATTERY in the locker, then break the boards to get outside.  
    You will meet up with Barney, who explains the plan to you while you 
    collect the two GRENADES in the truck to the right.  This next battle is 
    an endurance test, but thanks to the infinite rocket crate behind the 
    dumpster itís not terribly difficult.  Different waves of enemies will 
    spawn with each group of citizens you escort, as well as on each return 
    trip, and each requires its own strategy.
    -Group 1: There is no combat during the first trip, so take your time 
    and note your surroundings.  There is a lot of health on this path--
    three Health Stations, several MED KITS near the citizen waiting area, 
    and a small crate full of health--but no batteries, so donít be surprised 
    if you end this marathon with no Suit Power.  Alyx takes over the mounted 
    gun when you reach the end, providing cover fire and an easy way to finish 
    the Combine who try to follow you to the trains.
    -Return 1: Some Manhacks arrive in the station.  They are easy enough to 
    kill with the Gravity Gun, but their small size and numbers make them a 
    real pain.  There are more Manhacks outside, which you should lure through 
    the door for an easier kill, and three Hopper Mines are dropped from the 
    sky.  As long as you pull them up first, the Hoppers are great tools for 
    keeping the Combine at bay.  There are only two paths the Combine can take 
    through the trainyard; by planting both with Hopper Mines you can take out 
    lots of them before they can ever reach you.  To make them even better, 
    gather the three explosive barrels and place them directly behind the 
    Hoppers.  Once your perimeter is prepared, collect the next group.
    -Group 2: The Combine start to arrive now, but pretty slowly.  You can 
    easily sprint into the station and to the trains before they can land a 
    shot, and Alyx will eliminate the soldiers on your tail.  As a rule, you 
    should always sprint through the trainyard while you have citizens in tow.
    -Return 2: Assuming that Alyx killed the soldiers who followed you, your 
    first combat will be with a sniper who fires from the building across the 
    street.  (Donít forget to pull up any Hoppers between you and the rocket 
    crate.)  One well-placed rocket will smoke him out, after which you can 
    pick off the soldiers who rappel down the buildings for a while.  Place 
    your three new Hopper Mines now, including one between the crate and the 
    station entrance, then bring out the next group.
    -Group 3: Hereís where it gets tricky.  Inside the station a Combine 
    Elite will knock down the first train with an energy ball, stopping your 
    progress.  Kill him with a rocket, then lead them up the newly created 
    upper path.  Another Elite and soldier will land on the second train.  A 
    well-placed rocket can kill both of them, though you can spare a third 
    rocket if necessary.
    -Return 3: Once outside, large numbers of Combine will approach you on 
    foot and get blown up by your Hoppers.  On the far side is a tank, which 
    fires guided missiles at you until it is destroyed.  It takes four rockets 
    to do this; use the dumpster as a shield, and otherwise stay out of sight 
    as much as possible.  Finish off the troops who accompany the tank, and 
    you can collect the next group.
    -Group 4: This time the Combine will blow the lower door, then stream 
    into the station through it.  One rocket should be enough for this group, 
    though once you climb the ramp you will have to kill two more who jump 
    through the window.
    -Return 4: This one is a pure manpower rush: first a wave of Civil 
    Protection police, then a whole ton of Manhacks, and finally a large 
    Combine squadron.  The Hoppers can do a lot of the work, but you will 
    still get plenty of use out of your rocket launcher.
    -Group 5: Barney joins the final group.  Two more Combine land on the 
    roof of the train, and due to their spacing you will need a rocket for 
    each of them.  Refill your health before the doors are sealed.  If you 
    like you can refill your rockets one last time after dropping off the 
    last group, dodging bullets from the last few Combine, though it is by 
    no means necessary.
    *Part 2: Gordon the Giant Killer*
    -Batteries: 8
    -Med Kits: 4
    Barney says farewell, and you and Alyx set off to look for your own train 
    out of the city.  You will pick up two BATTERIES on the way forward.  Turn 
    the crank to let Alyx through, and the gameís final boss stalks toward you 
    at high speed.  Try to remain out of the Striderís line of sight until its 
    second blast, which opens the path forward.  Two soldiers will arrive up 
    ahead.  Since you probably only have one rocket (and you need to save it 
    for later), kill them by tossing grenades.
    From here you must make your way across the trainyard to higher ground, 
    while dodging the Striderís guns and the destructive effects of its 
    shockwave blast.  There is a Health Station at ground level, as well as a 
    BATTERY on top of the first layer of containers.  There is a pod of Poison 
    Headcrabs on the way up.  Wait for a blast to crack it open, then crowbar 
    both headcrabs when they come out.
    The next bit can take a few tries: you have to leap from a shipping 
    container to the walkway upstairs, a somewhat tricky jump that also 
    leaves you exposed to the Striderís guns.  You can count on taking damage 
    here, so just try to get behind cover as quickly as possible.  Once up 
    there, immediately grab the nearby explosive barrel and toss it far away.  
    Pretty soon the Strider will fire a blast at the catwalks which will 
    launch the burning barrel toward you, which is obviously bad news.  After 
    that is done you can recover at the Health Station if necessary.
    Your next trial is to sneak behind the panels for cover without setting 
    off the Hopper Mines.  While it takes some practice to do correctly, there 
    is a safe spot at the very edge of the panel which gives you time to 
    safely pull the Hopper out.  Another Soldier will fire at you from the 
    roof as you pull out the second Hopper; quickly toss it to kill him.  Move 
    quickly between the panels when the Strider stops firing, picking up the 
    two BATTERIES in crates as you go.  There is another BATTERY and a MED KIT 
    once you leap off the walkway, though you only have a short time before 
    the Striderís blasts end up crushing you.
    Hop downstairs onto a fenced-off path, and a final pair of soldiers will 
    arrive.  Kill them with a rocket, then back up to escape the burning 
    barrels that come rolling out of the shipping container behind them.  Pick 
    up the BATTERY next to their bodies, pull out the final two Hoppers, then 
    dash between the train cars to duck and pick up one last MED KIT and 
    BATTERY next to the fence.
    If you can survive the climb up the ladder, youíve basically won the 
    game.  Stay near the infinite rocket crate and behind cover, dash out to 
    fire between salvos, and after four rockets the infernal giant will finally 
    fall.  Head down the other ladder to meet up with Alyx, who gives you some 
    well-deserved praise before inviting you onto the train.  Step inside, wait 
    for Alyx to start the thing, and after a few seconds the Achievement will 
    finally appear on your screen.  Sit back, pat yourself on the back, and 
    enjoy the spectacular trip out of the city.  Your hard journey is finally at 
    an end, though Gordonís is just beginning.
    -bumcheekcity: The Gravity Gun Challenge FAQ he wrote for Half-Life 2 was an 
    excellent primer on the varied powers of the Gravity Gun (not to mention the 
    key to my successful completion of ďZombie ChopperĒ), and was a big 
    inspiration for this guide.
    -Valve Software: These guys have created some of the best-designed and most 
    fun games in recent history, and this one is no exception.  Hereís hoping 
    that they maintain that standard for many years to come.