Half-Life: Interloper

31st July 2012

The Replay Experience Experiment: Half-Life: Interloper

Gordon’s journey across Xen continues, but his supplies are running short, spent on destroying the Gonarch.

He also comes across the Xen army’s Alien Grunt cloning facility, where the army is created.

It can be noted that the Vortigaunts in one of the factories are not hostile towards the player, and will ignore him unless attacked.


No trivia known for this chapter

The Poll


The challenges below have been set by 2muchvideogames

  • Get to the teleporter in the first map without entering the cave.
  • Find a cache of 3 grenades (in the map with the tentacles.)
  • Don’t break any barrels in the factory.
  • Get to the top of the red-light tower.

MEDIUM: 100 Health 0 HEV [24KB]


Click on the thumbnails below to open a 1024 pixel wide image.
WARNING: The screenshots contain spoilers.

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The Replay Experience Experiment

This post is part of the The Replay Experience Experiment 2012 event. This is a chance to replay all the Half-Life games and discuss them based on our experiences since we first played them.

Hat Tip

All text taken from the CombineOverWiki, a fan-supported, editable wiki covering the Half-Life series of games.

A Complete Half-Life Walkthrough
A Complete Half-Life Walkthrough

On the left is a complete text walkthrough for Half-Life.

It has been written by Stanley E. Dunigan and updated with all the tricks and tips from PlanetPhillip.Com readers.

It is in PDF format, meaning you can open it directly in modern browsers or download it and print it.

(Left-click to open and right-click to save)

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  1. Summary

    Valve manage to do quite a lot of this chapter, you get to fight, run, jump, explore and general work hard.

    The problem is that I didn’t enjoy it much and this is quite important for a penultimate chapter. I don’t go into the final level feeling good about the game, although I understand why we need to have this chapter.

    Perhaps my screen is too small to really enjoy looking up as well as across for enemies. I also didn’t like the “forever spawning” nature of some of them. I much prefer to kill and relax but here I could really do that.


    I felt a lot of pressure in these levels and sometimes that’s good but perhaps the alien environment threw me off. I think there must be more upwards movement in this chapter than any other so far.

    Points of Interest

    I was about to write that there were no headcrabs but there were!

    G-man Sightings

    Nope, I don’t think so.

    Bugs or Errors

    None for me.

    The Poll

    I’m pretty sure I killed everything at least once, but a few times I did rush for the level change.


    – Get to the teleporter in the first map without entering the cave.
    – Find a cache of 3 grenades (in the map with the tentacles.)
    – Don’t break any barrels in the factory.
    – Get to the top of the red-light tower.

    I seriously suck at these challenges.

    5 Words or Less Review

    I got vertigo


    53 minutes



  2. Wesp5

    While I seem to actually be one of the few people who love Xen, as it finally was a really alien looking world and not a harmless version like e.g. in Unreal, what made it annoying for me and many others were the jumping problems. If Valve had kept the normal HL style with Xen one would have been much more satisfied in the end!

    1. Yes, I loved Unreal too, but I agree, it was the jumping around I didn’t like

  3. Xen is my favorite location in the whole Half-Life series. There’s nothing like exploring alien world which is different from ours. And this chapter gives the most exploration.

    In the first location we find ourselves in a big island with caves inside of it. There are traps – “mouths” on the ground. If we fall into one of them, it will spit us with great force, most likely we will then die from falling through great height. We can use the Xen “airplanes” to get to the teleporter, or explore the caves. Inside the caves, there are healing puddles, and strange alien equipment – “teeth” doors:


    and in the end, one of the cones will lower itself, and we will resurface on top of it. Then we will be challenged with finding least painful way down.

    Second location brings more excitement: we are on the even bigger island and there’s cool sky with two suns. Here we can see some alien equipment and alien slaves working with it. Long jump will come in handy when evading tentacles and gargantuas.


    Third location is a stunning change of scenes – we’re inside the alien factory where apparently they create alien grunts. Working alien slaves don’t attack us, which is a great touch, it allows to see how they work, which aids the exploration spirit greatly. It is so heavily guarded, howewer, that even infinite healing machines fail to prevent me from dying.

    Finally, we see the teleporter under the ceiling, and elevators which lead to it. But if we go to the red hole in the wall, we find ourselves in a very imaginative area with spiral walkways.


    And the last location is the smallest. It’s the creepy place where some small islands float in black void. Big teleporter is obviously our goal, and for some reason we hear scientists” voices coming from it “Get him out of there, shut down the equipment and someone get him out!”.

    Overall, level design in this chapter is the best in the whole Half-Life series: very various, beautiful and imaginative.

    Playtime: 32 minutes

    1. we are on the even bigger island and there’s cool sky with two suns.

      You do realize that it’s a reflection right? they made the bottom part of the skybox EXACTLY like the top part (or used a reflection function if there is one, you’re the mapper, not me) so that we are confused about the islands, are they really floating? are they on some reflecting liquid? what is this sky made of? where do we fall when we die?
      There aren’t 2 suns, there is a sun and it’s reflection in thin air, which makes it more weird.

  4. William

    Playtime: 31:41

  5. Ade

    Anyone else notice the resemblance between the Xen thumpers and the antlion ones? 😀
    This was a hard chapter for me back in the day and even today, til in the fast rotating platforms level I decided to use the hivehand to kill the controllers and vorts who suddenly decided to attack!
    Am so proud of myself that I did all challenges, small gift to me for my bday, next: icecream!

    Playtime: 52 minutes, beat ya, Phil!

    1. Stanley Dunigan

      Actually, I think those two thumper-like machines near the alien slave cave in the second part of Interloper are meant to be energy drills of some sort. It’s extremely rare for some reason, but I remember that in a few past playthrus of the game, I’ve seen those machines “push” little green rings of energy up into the sky. I don’t know why those energy rings usually don’t display, but I think they’re always meant to. (Perhaps they only work in early patch versions of the original game. It has been a long time since I’ve seen them.)

    2. actually, valve stated that they didn’t know themselves what those thumpers were for at first, but decided to put them here so people would think there was something intelligent going on in xen even before seeing the grunt factory. Like some minerals extraction or something. then when they made half-life 2, they decided to make combien thumpers to repel the antlions that could burrow, and decided that those hl1 thumpers would officially have this use too. since no information was given on the hl1 thumpers, they could decide what to make with them after, and it would be canon. now we can assume that there were many antlions on xen, but that they were not friendly to some other xenians (as the bullsquid hates headcrabs and other bullsquids) so they repelled them from some locations. In hl2, when you get the bugbait, you can make the antlions beat up headcrabs and zombies, but it is unclear if they will attack them when you don’t have a bugbait (none can be encountered at the same time before getting bugbait).
      I guess the headcrabs have a bad reputations among other xenians, so many other xenians hate them.

      1. Interloper

        The “thumpers”, like many other aspects of the game, were built and placed by a designer to help guide the game’s design/tone and story. As a side note, their design is meant to resemble that of a phage virus. These, and the rest of Xen had much more design behind it but resources and support for the alien world were extremely limited. The team was working on the rest of the game while a single designer cranked out the majority of Xen, style and all, from scratch. The only mandate given was that it had to include a lot of jumping puzzles. :/

        It’s very likely the least tested portion of the game.


    I remember finding the ” factory” area of this chapter to be very difficult. However by one-shoting Vortigaunts and two-shoting Alien Controllers with the Magnum and not breaking any of the Alien Grunt pods, it didn’t prove too difficult this time around.

    Playtime: 32 minutes

  7. 2muchvideogames


    Bloopers: http://www.youtube.com/watch?v=fpHZGyU2PzQ

    This is a quite long-winded chapter in an alien, unfamiliar setting. Strange, discoloured textures are everywhere, and the sky backdrop is also very weird indeed. The Xenizens are throwing everything they got at you: tentacles, gargantuas, horrific timed jumps, everything. I died 3 times on the first map trying to get the first challenge. For the later maps, it’s important to move carefully rather than quickly, since one missed jump and the autosave takes you back to the bottom again.

    Then again, I wonder how valve was going to make Gordon ‘lead” the vortigaunt rebellion on xen. Another mystery for you HL fans.

    Playtime 11’40”

    1. there was no vortigaunt rebellion. the vortigaunts are neutral creatures, that have been enslaved by the nihilanth and it’s minions (controllers). that explains why in the factory they don’t attack us (they work) but later when a controller shows up, they attack (he gave them an order?). In hl2, they are so thankful to gordon to have killed the nihilanth (and made them break free, but gordon didn’t know that at this point) that they decide to take the human’s side, and help gordon a lot. Also the combien is suppoesed to have invaded the xenian’s homeworld, so they fled to XEN and then the combien was approaching when we opened the dimensional breach, so xenians took this as a chance to escape the combine.


    This was a cool chapter. We get to see where the Alien Grunts come from and can even keep peace with the Slaves (for a short time). I liked the little touches like the sprites in the air in the “vents”. Some of the ceilings look like the same texture as the Gonarchs Shell. I really liked the voices coming out of the red portal at the end.

    Dreamcast differences

    The first map of Interloper is missing. It was probably taken out because it would be very hard to play that level with a controller. Also, at the part where the barrel(s) are blocking your way, there is only 1 barrel instead of 2.


    Like Surface Tension, there’s a part where the texturing before the level change doesn’t match up with the texturing after the level change.

    Playtime: 7 minutes
    5 words or less: Panic in Xen

  9. I don’t know if it’s just me or the entire youtube, but uploading doesn’t work for an unknown reason. If anyone knows what to do when it says that the server didn’t send a response (about middle of upload), check the troubleshooting page. this makes me start over, and did it to me 8 times (I tried re-producing the video in multiple other file types) so I gave up. I’ll probably manage to upload it in a few days, until then I’ll give you the review and the playtime, you just can’t look at it. I will post another comment here with only the link when it will be up, so phillip can embed it and link it to the main TREE page.

    Interloper is the last real combat chapter, since after that it’s the boss fight. We start up on a small floating island right over a huge one, and ours will break prety quickly no matter what we do, so we fall. No fall damage here. there are many holes in the ground that will “swallow” you then “spit” you out really high. there are some weird alien towers that go up and down, and many alien dropships and moving island (like in the first xen chapter). the dropship drops many alien slaves at you, and there are controllers spawning in the air.
    I skipped almost this entire map by making a grenade jump at the beginning, but I know that you’re supposed to enter some caves, kill some bullsquids and barnacles, swim in weird water, and get on top of one of the towers, then do some jumping puzzle to get to the teleporter.

    In the next map, we see some tentacles, and it’s pretty obvious that the grunts on top of the hills are guarding the place, suggesting they really are the xen fighters. you can find many dead bodies, suggesting once again that you are not the first one to come here. then a garg opens the way, some more jumping with tentacles attacking you, then you reach the teleporter. then you get in a factory, where for the first time, slaves are neutral. when a controller is present, they will become hostile. you see some barrels, some empty ones, and some other with blood on them that contain a grunt. we get on the alien conveyor, fall in some water, then run around like freaks to find the exit to this place crowded with ennemies. we encounter the healing cabin, that the slaves will use if they are hurt, suggesting that the xen pools will also heal them if they got in. I made some tests, and gordon must be some sort of special human because barneys and scientists will NOT get healed by those.
    Then we get in some weird vents with orange things floating around.
    then we get in a large room with a very high ceiling with a teleporter. the elevators come in handy, but make me a bit dizzy. Also the teleporter in the ceiling brings in controllers, which is weird since when you get in, you are brought to a floating platform without any mean of going back, nor any controllers present. then some more jumping and we reach a weird red teleporter that makes noises
    the noises are obviously some scientist’s sentences from the beginning of the game, and even throughout it. That makes us wonder where do the souls of the killed go?
    then we teleport on the the Boss.

    – Get to the teleporter in the first map without entering the cave.
    Got it right, in about 1 second and a half 😛
    – Find a cache of 3 grenades (in the map with the tentacles.)
    i didn’t but I know where it is. it’s next to the room the garg comes out of right? in a small cave
    – don’t break any barrels in the factory.
    I broke one, because it was faster than jumping over it
    – Get to the top of the red-light tower.
    I have no idea what tower you are talking about, but if it’s the last teleporter it’s pretty easy to go on it.

    Five words or less review:
    Last room is too damn high!

    none 😀 I’m happy because I’m am really confident to survive the nihilanth, so that means I will only have died 4 times total 😀

    5 Minutes 22 Seconds 83 Milliseconds

    PS: my skill level was going downhill throughout my video. I was super fast in the first 2 maps (got to the first teleporter in about 2.75 seconds) and ran through the second one at a great speed. I was also pretty fast in the next one, but then my playthrough was about like the average player for the rest of the time. I’m glad my aim was good because I wasted so much time killing monsters and healing to not die that I could not waster any more on missed shots.

    1. Ade

      for the missed challenges just watch William’s playthrough

    2. I finally managed to get the upload to work!

      Not sure if anyone will see this link since the chapter’s TREE is so old, but here it is anyway

  10. Interloper (German: “Eindringlinge”)

    Finally this chapter is over, I admit I hate it, especially on hard.
    However, when revisiting it I tried to complete all challenges and was searching every corner and dark spots for goodies as I just wasted a lot of ammo here and health gets critical quick when facing many alien slaves and / or alien controllers.

    But that’s not the worst, what I dislike most is the design, sure it’s some futuristic foreign world, but I’m not a fan of that, looks like some Star Trek stuff, not sure.
    Therefore I tried to get through as quick as possible. Thanks god for the healing stations! Died several times (tentacles, getting squished, alien slaves, alien controllers, being out of space 😛 )

    So yes, as I’m not liking “Interloper” I barely could remember the places where alien slaves are, so that was surprising sometimes and even causes some instant deaths when more than one appeared 🙂

    What’s cool is the ambient sounds and the outdoor areas, the tentacles can get nasty but nice placement of them, also for the Garg who’s unfortunately acting a little stupid here, for example punching into air or just ignoring me.
    Guess the AI is not that good this time.

    In the last part of the factory the last elevator didn’t came down and I thought it’s bug as there’s no switch, but then I decided to try going back to the red-light tower and killing the two alien controllers which I left behind after being on top of the tower. That somehow worked, the elevator came down…

    All in all I’m truly glad this is over, the factory is just terrible for me, the first part outside and in the caves is pretty nice and also tough, but way better than factory in my eyes. Altho, layout is not bad there too I have to admit.

    Remembering playing “Interloper” the first times, I just couldn’t figure out how or where to proceed sometimes, fortunately it’s all clear today 😉

    Bugs: Elevator bugs, got stuck more than once and the last one in the factory didn’t came down first, I dunno what’s the trigger for it…

    Poll: Voted “kill most enemies and move quickly”, while “move quickly” has to be defined to “move more carefully than usual”

    Deaths: Quite many, around 10


    -Get to the teleporter in the first map without entering the cave. – No
    -Find a cache of 3 grenades (in the map with the tentacles.) – Yes
    -don’t break any barrels in the factory. – Yes
    -Get to the top of the red-light tower – Yes

    5 words or less review: The Great Escape

    Playtime: 37 minutes

  11. Stanley Dunigan

    I have many clear memories of playing this chapter years ago, mainly because it was so “alien” and difficult. The first section, where you’re on the floating island with the cave and the “elevator spire,” is still one of the hardest parts of the game for me.

    I remember years ago, when I first started playing the game on the highest difficulty setting with no cheats, I considered the teleporting-out sequence at the end of the “Lambda Core” chapter to be the first of three parts of the game that are the absolute hardest. The second of those hardest parts was the second stage of combat with Gonarch (the “easy” strategy of dropping down into the pit and shooting up at Gonarch often caused a glitch that made the thing invincible in early patch versions), and the third one was the first stage of “Interloper.”

    While writing and improving my “ultimate” strategy guide for Half-Life, I’ve come up with strategies for all three of those parts of the game that make them pretty easy (though they still often require several retries). However, I still get really nervous when I know one of those parts is coming up. I guess those are my Half-Life replay reflexes kicking in!

    To answer the poll question, my usual strategy in Half-Life (and other shooter-type games) is to play conservatively. My top priority is usually to take as little damage as possible, with a secondary priority of using as little ammo as possible. “Kill everything and move carefully” is the poll answer that most closely matches up with that, though I do handle the first part of “Interloper” differently. These days, I always use the strategy of doing a long jump to the alien flyer that appears near the stationary floating rock. I then AR-grenade any vorts that are close enough to zap me while flying to where I can long-jump over to the teleporter. So in that case, I kill few enemies and move as fast as possible.

    For the rest of the chapter, I play more slowly and conservatively, though I’m not averse to skipping areas that have only enemies in them and no supplies at all (or only a health pack or something else that I don’t need.) Take for example the second part of the chapter, after you ride a barrel-carryin” conveyor belt to where you drop down into a small tank of liquid. After dropping to the floor and finishing off all nearby hostiles from the corner with a grunt barrel in it, I ride the little triangular lift back up to the barrel tank’s edge, but I don’t go along the side walkway and through a barrel conveyor area. Instead, I jump across to the two nearby up-and-down piston thingies and go from there. That skips zero supplies, plus several vorts and controllers. That’s what I consider to be the “good” kind of shortcut.

    As for the four listed challenges, I already described how I did the first one (long-jump to flyer). With the second one, I know where those grenades (and an armor battery) are, but I never need them when I get to that part of the game due to my conservative play style, so I always skip them. I never do the third challenge, since I long ago got in the habit of breaking just about every grunt barrel and horneting their grunts to death (while hiding around a corner to hopefully avoid taking fire).

    The reason for that is there’s a glitch in just about every version of the game (except the Source version) where grunts can “go active” and start firing hornets at you even if their barrels are unbroken. That happened a *lot* back in the early days, so I got in the habit of breaking all the barrels and killing the grunts “just in case.” The fourth challenge refers to what I call the “spiral-screw-style room,” and I always visit it for the armor batteries that are on its top platform. You can always drop quickly down the pathways and escape before the controllers get you. (Or you can play the Source version of the game, in which there are no controllers in that area.)

    My playtime for this chapter is always really long (I never keep track). I usually don’t get killed anywhere, though I do often have to quickrestore and try something again, like if I miss the long jump to the alien flyer in the first chapter section. The elevator glitch (where you get stuck and slowly take damage) used to be a *major* pain in the area where you have to ascend to a big rotating teleporter, though both versions of the game on Steam seem to have pretty much eliminated that glitch. Five words or less review? Ummm… how “bout: XEN IS A FRICKIN” PAIN!

  12. Unq

    Interloper is of course the real heart of Xen in Half-Life, when people complain about Xen I always see them as complaining about this chapter specifically. I can see why people don’t like it, but in taking a good look at Interloper this time through, I actually think it’s one of Half-Life’s absolute best chapters and is certainly one of my favorites.

    First of all, damn this chapter is a bitch on Hard! I complained in the July General Chat about Half-Life being a cakewalk on Hard, but I think Interloper gets it right. I died a bunch of times, but only half were from falls. On Hard, the slaves are quicker on the draw and a couple together can take you down really fast if you’re in the open. I honestly wish the rest of Half-Life were this challenging on the toughest difficulty level.

    The brilliance of Interloper is that Valve makes you feel like the alien. This part of the game has a different look and a different feel – ultimately making the gameplay very different. This was a brave move on Valve’s part. I think it achieves a great contrast to the rest of Half-Life (essentially Black Mesa), but I understand it’s not as fun to play – I like Xen, but I don’t think it’s better than Black Mesa, I just think it serves as a fantastic contrast rather than taking the easy road and keeping the whole game in Black Mesa.

    Let’s look at the claim “the gameplay is different” for a second. It’s simply wrong to claim Xen is all jumping puzzles. There are really only a handful (and mostly in the first and last maps of Interloper), although through much of this chapter there are falling risks, they’re not the focus. The true focus is really the vertical dimension. Before Interloper, really the only vertical combat maps we’ve seen were the dam and the cliff in Surface Tension. Interloper is full of these areas, and the second to last map is basically a pure ascent to the teleporter at the top. It’s difficult and it’s different. You are the interloper here, not welcome.

    Mapper’s Corner: The opening map of this chapter has a number of tricky little trapdoors that can open under you, hurt you a bit, and then launch you a good distance above the Xen surface.


    – The “mouths” that constantly open and close are in fact 8 func_doors that are triggered and retriggered at set intervals. They are each wedge shaped and fit together when the mouth is closed like a sliced pizza.

    – The devilish part is that surrounding the hole, there are a bunch of trigger_push areas that “encourage” you to fall in (they’re about where the small slopes are around the hole). There’s also one over top of the hole that pushes you down so it can kind of suck you in if you jump over the hole.

    – The areas have func_monsterclips around them (invisible in-game) to stop the vortigaunts from falling in. Too bad, hilarity would ensue.

    – When you do fall in, you touch a trigger_multiple that targets a multi_manager that handles the rest of the sequence:

    1. A short env_shake to shake the screen a little, with an accompanying sound (ambient_generic) to make it sound like you’re being digested perhaps
    2. After a short delay, a trigger_hurt to do 10 damage to you before really punishing you
    3. A trigger_push (with accompanying “bounce” sound) that shoots you way, way up in the weak Xen gravity. You’ll be lucky to land somewhere that the fall won’t make you go splat

    Playtime: 38 minutes

  13. This chapter was a lot of fun, and after reaching the factories I really had a feeling that there is no turning back, and that I have to bring Gordon’s mission to an end. I rarely feel this in games, sadly, and I’m glad Half-Life managed to do it.

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