Above Good and Evil: Alexander expresses disdain for concepts like "good" and "evil", thinking them only good for comfort and not something to be concerned about. He reminds Daniel that they are Not So Different after Daniel calmly went along with Alexander's plans to torture and kill in order to preserve his own life from The Shadow, and thus Daniel has no better claim to "goodness" than he does - sidestepping that Alexander preyed on Daniel's desperation to convince him it was necessary.
Absurdly-Spacious Sewer: Apparently justified by being used to carry spring water which surges seasonally. It also functions as a cistern system to retain excess water and carefully control its pressure to power water mills.
Advancing Wall of Doom: The Shadow of the Orb manifests as an advancing wave of decay and corrosion that you have to run away from at certain key points in the game.
Alien Geometries: The Choir and Chancel towards the end of the game are...peculiar. Daniel also has visions of these when he first finds the orb.
Always a Bigger Fish: An offscreen variant. Boy, that Grunt sure is scary, isn't he? You can't do anything to stop him and if he finds you you're dead in moments. So exactly what was capable of dismembering one so easily?
Artifact of Doom: The Orbs. If, for whatever reason, the individual who discovers one is unable to master its power, then the Shadow that guards it will relentlessly pursue him, killing everyone he encounters in the process.
Artificial Stupidity: One of the few breaks you'll ever get in the game when encountering monsters. Most of them have horrible vision when you're not in light, get bored chasing you after a while, or are generally unable to notice you when you're literally right next to them. In areas with bottomless pits and other falls, you can lure them to falling to their death (despawn). Also, they cannot attack you if you're on top of them or they are somehow stuck on top of barrels, and they can't see you if you can't see them. Probably justified in-game - the monsters are described as "feeding off your fear" in a way, are more likely to see you if you keep staring at them, and their strength is dependent on your mental strength. If you're good at avoiding them, don't expect much Artificial Brilliance.
Arson, Murder, and Jaywalking: As you learn about various torture victims, the severity of their supposed crimes seems to lessen. The worst were accused of rape and arson, but a forger got thrown into the iron maiden as well.
Artistic License - Biology: When Daniel has to vaccinate himself with a corpse's blood. God only knows if they're the same blood type or if he had any infectious diseases. At least upon touching the body while not holding anything it states that it "Can't be more than a day old." Still, as Lanipator puts it in his Let's Play: "The least sanitary thing I could possibly do!"
According to Amnesia, combining aqua regia, orpiment, cuprite, and calamine all togethernote no idea how much of each, which one goes first, etc. creates simply "acid". No, the pH isn't known either. Note that Aqua Regia is already a mixture of nitric and hydrochloric acid capable of dissolving gold. Why you must add a copper-based mineral (cuprite), Arsenic Trisulfide (orpiment, once used for poisoned arrows) and Zinc Oxide (calamine, used in cosmetic creams and powders) is up to you to guess, when royal water alone would have done the job of dissolving organic tissue.
After you use the "acid" to melt the organic tissue, the container it was in isn't washed out, and is re-used for something else later, despite the traces of acid. Even worse, later in the game, Daniel finds a glass jar. He uses it to transport acid, then oil, once again without washing it out. After that, he can use it to prepare Weyer's tonic — the potion Agrippa's survival depends on.
Artistic License - Physics: You can light candles and torches that have fallen over and are lying sideways. If you do, the flames still shoot out parallel to the barrel of the candle or torch (i.e. sideways, instead of towards the ceiling).
Asshole Victim: Daniel or Alexander, depending of the ending. Either of these two qualifies. Redemptive attempts aside if we talk about Daniel - he was not even an alien as Alexander was, and even Alexander himself feels a little surprised by him.
Beethoven Was an Alien Spy: Agrippa and Weyer were real historical figures, Agrippa being a 16th century alchemist and Weyer being his apprentice. This game indicates that Weyer, like Alexander, actually came from... elsewhere...
Agrippa was also an occultist in Real Life, about 300 years before Amnesia takes place. He 'presumes' that he was held prisoner by Alexander for hundreds of years, which would make the numbers match up.
Just try looking at the monsters or Agrippa without cringing a bit at the thought that they all used to be men.
In the sewer beneath the castle - in order to keep from being killed by poisonous fungi, you need to drill a hole into the head of a corpse, insert a needle into a copper tube, insert that tube's base into the skull, and then stick yourself on the needle to immunize yourself. That's Body Horror, Afraid of Needles, and a makeshift transfusion all in one scene.
Brain Bleach: The player will feel like they need one after visiting some of the later portions of the game. Daniel himself eventually needs (and uses) some after the weight of all the things he's seen and done catches up with him, and he is forced to ask himself whether he can live with knowing it.
Breather Level: The Back Hall. It's downright serene and pleasant compared to the Archive Tunnels you have to run through to get there... at least, until giant fleshy tumors sprout everywhere and the fountain starts pouring blood.
The Back Hall portion was discussed in the Dev commentary, in which they invoked this trope, going along the lines of "This is meant to relax the player a bit so the upcoming horrors will be even worse by comparison."
Also the main Cistern area and where you meet Agrippa in the Nave, which works as a breather room.
Collapsing Lair: At the end of the game when you exit the castle, if you look behind you, you can see rocks completely obstructing the way back to the Entrance Hall. Also, you can hear crumble noises while Daniel opens the big door.
Collision Damage: The Meat Moss hurts you if you stand on it, though it is possible to jump on and off it fast enough to avoid damage.
Comedic Sociopathy: The game is horrifying to play, especially alone at night, but watching other people play it while freaking out is inherently hilarious. You will probably be whimpering/screaming profanity during gameplay, but that doesn't stop it from being terribly amusing. Playing it with observers on On Live is a good example of this.
This one might be the best known, and is notable for being the source of the minor fandom meme "Oh shit, I have a bag of Milky Ways."
Companion Cube: Not so much on Daniel (the player character)'s part, but many players will find and cling to some item in the environment as a security blanket- for example, Pew Die Pie often picks up (and talks to) random objects, naming and giving them voices, as a self-comfort measure.
The lantern may be this to some players considering it is a source of light that is always with you through most of the game and helps maintain your sanity.
Cower Power: Literally, the best way to survive a monster is to find a dark corner, curl up with your nose to the wall, and pray it leaves before it stumbles over you. Justified, as Daniel has no means by which to fight back against these monsters, they can generally outrun him when they break into a sprint, and closing doors will only slow them down at best.
Delicious Distraction: The water monster can be briefly placated by chucking one of the many severed body parts lying around into the water.
Doomed by Canon: The written supplementary materials focus on characters who were mentioned in-game as dying or disappearing without a trace. Each story ends right before the event that kills them.
Doom Magnet: Everywhere Daniel goes, people die. It turns out it's the Shadow hunting him. By the time the games events begin, he is almost a Walking Wasteland.
Downer Ending: The bad ending, in which Daniel dies and Alexander gets away scot-free with everything. Many of the custom stories also have downer endings:
The Things In The Night: After Fin kills the Evil, the Shadow's Expy,and then confronts his father, there are either the choices of joining him or kill him. The former will trigger the ending in which the father traps Fin in a cage filled with Grunts, killing him, and the latter results in an ending where something is shown busting the door to the room Fin is in, revealing the Evil survived and is implied to kill Fin.
Tenebris Lake: Edward can either save himself and leave his family to die in the crumbling remains of the house, or save his family and die by falling debris.
Disponentia: The protagonist escapes the cursed house, but upon jumping a fence, he is chased by ferocious dogs and when trying to find sanctuary in a nearby house, he is denied entry and mauled by the dogs.
White Night: The psychologist is revealed to be the Big Bad and purposely keeping the patients in the institution to perform experiments on them, and in the end, the protagonist gets captured and the psychologist gets away with everything.
Down the Drain: There is an awful lot of this, including an invisible monster that devours you if you touch water, just to give all subsequent drain sections that little extra touch of paranoia
Dramatic Spotlight: During the Archives bit, there is a (barely) playable flashback from when Daniel first laid hands on an Orb, during the expedition in Algeria. There is a pedestal with the Orb on it, in a circle of light. Everything else is darkness.
Dummied Out: Apparently, the character of Daniel's sister Hazel (though occasional references to her are still present in the above mentioned developer's commentary and in some late-game Loading Screen notes).
DVD Commentary: Developer Commentaries are able to be toggled, and appear in-game in the form of the Frictional logo (a 6-sided gear) surrounding a microphone. Since most players will want to go the first round without the commentary, this gives a bit of a boost to its replayability. The commentaries are a Pre-Order Bonus.
Easter Egg: See that tiny six-digit code at the bottom of the screen when you finish the game? Get all the endings and write down the codes, because you can use them to unlock the "super secret" .rar file in the game folder, containing Concept Art, design documents, Dummied Out audio and footage of the game's alpha versions.
Evil Mentor: Part of why Daniel finally snaps in the first place and drinks the amnesia potion is because he learns that not all of the Baron's victims are criminals... victims that Daniel has happily tortured in the past.
Eye Scream: One of the flashbacks in the Torture Cellar contains this... thankfully in text form, but given the limitations on character models, that might be worse.
Facial Horror: If the player is caught by a monster, this is likely to be the last thing they see. Also applies to Agrippa, though his friendly attitude tends to undermine the horror after the initial shock wears off.
Fission Mailed: Near the end, where Daniel is captured and put into a prison cell. Complete with a special game over message!
Flower Motifs: Roses. The "amnesia" potion is made of oil-of-roses, and rose petals appear at key moments when memories start to return to Daniel. And when he goes through the gate.
Food Chain of Evil: As you head into the second half of the game, you find the grunt's eviscerated corpse on the floor and are left to the realization that now you get to run from whatever did that.
Game-Breaking Bug: The game flat out refuses to run on anything except very specific video cards.
Note that the first patch remedied this to some extent: Amnesia now runs on any GeForce 6 or higher Nvidia card, or any Radeon x1300 or higher.
Glass Cannon: The Kaernk, that invisible monster, can tear the player up, but can be killed by simply throwing a box on it. Good luck hitting it, though.
Golden Ending: By tossing Agrippa's severed head into the portal, Agrippa gets through the portal, leaving Daniel and Alexander trapped in the Inner Sanctum. The Shadow kills Alexander and apparently kills Daniel too, but Daniel is drawn through the portal by Agrippa before he truly dies. Agrippa (alive and well due to the potion Daniel gives him) and Weyer both begin to tend to Daniel's wounds. Agrippa tells Daniel "everything will be alright," implying they will bring him back from the brink of death, and give him the potential Immortality they have in their world.
Hazardous Water: The archives under the castle are all flooded knee or waist deep. Unfortunately for Daniel, that is the only environment in which invisible, flesh-hungry monsters from another dimension can survive...
Heel Realization: Daniel, once he finds the final Diary entry - the player will realize it beforehand, though.
Hollywood Darkness: Completely shattered - if you try to peer into a dark room from a lit hallway, you will see nothing beyond the doorframe.
Played around with throughout too; a lot of areas do have subtly blue ambient light, and standing in darkness helps Daniel see in the dark in bluish hues, but then there's an area with no ambient light at all that is stated to be "unnaturally dark" and areas with similar lighting appear throughout as a sign of incoming horror.
Ill Girl: Daniel's sister/cousin will either have died or survived depending on how "kind" you are in the game. (She is only mentioned in loading segments.)
Immortality Immorality: It's strongly indicated that the Baron, being stuck in human form, needs vitae (cosmic life force) to prolong his life until he can find a way back to his own dimension. Unfortunately, the only viable source of sufficient quantities of vitae is the prolonged torture and agony of human beings. Daniel, likewise, needs to regularly perform human sacrifices to keep the Shadow at bay.
Interface Screw: As your sanity decreases, the screen distorts, as if you're looking through a thin layer of water. At really low levels, Daniel's movements lag behind your mouse movements.
Subverted as there isn't actually any threat yet. It is played straight when the game tells you about being able to hide in cupboards though.
Ironic Echo: Fail to escape the cage filling with Meat Moss and you hear echoes of other Brennenberg prisoners pleading for mercy. Their fate is now yours!
Just One More Level: A design decision. The game's levels were designed to be short and bite-sized to provoke this effect.
Large Ham: The guy they got to voice The Baron seems to be really into it. Some of his line readings border on mood breaking, especially a couple at the very beginning of the game, most notably the first time he says "The Inner Sanctum".
"...in fact, it lies beneath the very stone of Brennenburg!"
Leitmotif: Each character has their own associated piece of theme music. Each piece has several variations to represent different moods. Most commonly this can be heard while reading notes written by various characters. Specific songs also "give away" when a monster is lurking around, and of course, the screech when a monster is actively chasing you.
Let's Play: A popular game for LPers due to the audience wanting to see them scared. One particular one is by Helloween4545.
Lightning Bruiser: The Brutes. They run faster than Daniel and can kill him in one hit.
Karma Houdini: Both Daniel and Alexander depending on the ending.
Though, some endings can be interpreted as the Shadow brutally killed Alexander and leaving Daniel alone completely. He had gone through Hell via the entire ordeal of killing Alexander and that was his penance, so to speak.
However, the definitive example, in the Justine expansion, is Justine herself.
Multiple Endings: If you break Alexander's machine before it opens the portal, Alexander dies and Daniel leaves Brennenburg free of his curse and content that he did the right thing. If you let the portal open and didn't help Agrippa, Alexander will go through the portal and the darkness will kill you. If you let the portal open and throw Agrippa's head through it, both you and Alexander will die, but Agrippa will call out to you in the ethereal realm and ask Weyer to help you, before assuring you "it will be alright."
Musical Spoiler: You can easily tell if the enemies are nearby or still chasing you.
Averted when hiding from monsters, the music will still play until you man up and make sure by yourself that the monster is gone.
Mythology Gag: In the intro, you get a throwaway reference from Daniel about him living in Mayfair, London. That's the same place where the protagonist of the Penumbra series goes to retrieve the heirloom of his missing father (which kicks off the plot of the first game).
Also, the "memory capsules" are very similar to the Tuurngait artifacts in Penumbra.
No Budget: Would you believe that Frictional Games, the developers of Amnesia, had to work for no pay for a month or two? It's impressive that it turned out as well as it did, given their methods of motion-capping the monsters.
Nothing Is Scarier: In spades. The monsters are scarce enough to keep them from being a source of frustration, but frequent enough to ramp up the terror. Add to that ambient sounds that, at times, sound like footsteps, and you'll be cowering in a corner for fear of a monster you haven't even seen yet. The game doesn't even let you get a good look at the monsters, ever, because just looking at them drops your sanity meter and causes the screen to blur... and makes them notice you.
The splashing water scene. A lot of players claim the scene nearly gave them a heart attack.
Yahtzee: Amnesia understands that a monster stays scary the less you see of it.
One of the measurements of your low sanity is simply "..."
Ontological Mystery: The beginning of the game. After you struggle through a few corridors and staircases, you find your notes and learn a bit more about who you seemingly are and what you supposed to do after willingly inducing amnesia on yourself.
Powered by a Forsaken Child: Vitae, a substance containing the cosmic lifeforce Baron Alexander needs for his alchemy, can only be obtained through the prolonged torture and suffering of human beings. This, more than anything else, is why Castle Brennenburg is such a gallery of horrors.
Baron Alexander: As long as the body suffers, it will continue to produce the vitae and saturate the blood with its properties.
Primal Fear: Plays heavily on several of these. Fear of the dark is, as the title suggests, a frequent one, but that is also subserviant to a more general fear of the unknown. The game uses lots of little tricks to ensure this fear is invoked, such as noises to suggest what might be near, and Teleporting Key Card Squad to ensure that monsters can be anywhere, and Nothing Is Scarier to keep players tense and on-edge. Even if one tries looking at the monsters (Body Horrors though they are) Daniel's vision will be blurred and distorted, ensuring that they retain an element of mystery and unknowability, in addition to their role as predators after helpless prey.
Redemption Quest: Not revealed until the final Journal entry, but strongly hinted at prior.
Roaring Rampage of Revenge: Became Daniel's motivation to kill Alexander for manipulating him into torturing and killing innocent people all the while never intending to protect him from the Shadow in the first place.
Run or Die: Your only two choices when a monster spots you.
Sanity Meter: The bad thing is that it's an accurate barometer of the player's mood. Well, except for needing to stay near lights to keep sane.
Scenery Gorn: The decaying ruins of Brennenburg. It progressively gets worse once the Shadow starts taking over.
The torture chambers and the Choir.
Schmuck Bait: Go ahead and hop inside the Iron Maiden in one of the torture rooms. See what happens.
Try lighting a fire under the Brazen Bull in the Choir. You won't get hurt, but your sanity will take a nasty hit. And the Choir is the absolute worst place to have low sanity.
Shout Out: Daniel's backstory, wherein he loses his memories of a large portion of his life and is involved in exploring an ancient set of ruins hidden under a vast desert which contain Alien Geometry, is reminiscent of the HP Lovecraft story The Shadow Out of Time.
Story Breadcrumbs: Diary entries, miscellaneous documents, and the occasional flashback.
Strong as They Need to Be: Most of the terror of the game comes from the fact that you're playing as a regular human who lacks any skill or ability that would allow him to fight back against the creatures stalking him. This is somewhat undermined by the fact that Daniel seems to be crazy strong, judging by various puzzle sequences in which he busts open stone walls with a shovel or smashes through foot-thick wood pillars with his bare hands. He also has no problem picking up and throwing large rocks and boulders (some bigger than he is) - but struggles to open a perfectly normal wooden trapdoor. Perhaps it's made out of plot, well-known for its resistance to even the most panic-boosted strength.
Also discussed in-game in one of the notes. Given what Daniel's facing, it's not surprising he can pull it off from time-to-time.
Baron Alexander: Even the most timid creature can break out in fits of violence where their strength exceeds their expected prowess.
It also bears mentioning that, in those particular instances, the wall or floor has already been weakened to the point of the mortar being loose enough for it to happen.
Sympathetic Murder Backstory: Daniel is manipulated by Alexander into sacrificing what he thought were criminals. He is devastated after he was forced to kill a little girl, and nearly loses his sanity. He vows revenge on Alexander for that. Amongst the flashbacks in-game involve the cries of the lives he took (children's voices were amongst them).
Tactical Door Use: Doors will not stop monsters, but they will slow them down, requiring several Barrier Busting Blows to batter down before they can enter. This is essential in some scenarios for buying Daniel extra time to put distance between himself and the threat or finding a better place to hide.
Talking to Himself: There are only two, somewhat minor examples. The first is Wilhelm and his companions in the Wine Cellar - all are voiced by Dan Zullo. The second is the dialogue between the girl Daniel murdered and her mother in the prison - both characters are voiced by Lani Minella.
Technicolor Science: The acid is bright, glowing green. Even without a heat source, it boils dramatically to the point of hurling out glass bottles dropped in it.
Teleporting Keycard Squad: Unfortunately played straight some of the time: generally, when there's a puzzle-relevant object in plain sight, you can bet that a monster is going to spawn two rooms back to terrorize you after you pick it up. Of course, knowing this makes it even more tense, because you'll be afraid to even find the solutions because you know they could cause a monster to spawn.
To quote Yahtzee again: "It's like they're being summoned by the autosave function."
The Reveal: Why Daniel is in the castle, of course! It wouldn't have the amnesia factor without a reveal as to how he got there, after all.
Through the Eyes of Madness: The paintings, especially the portrait of Baron Alexander, change as your sanity gets lower. Although, given that he is explicitly stated to be from a different world, this might actually be a somewhat bizarre case of Glamour Failure.
Throwing The Distraction: Enemies react to sound, so this is a good strategy to get them to wander in the direction you want. It's also entirely necessary to pass one particular enemy.
Title Drop: A note discovered late in the game indicates that the elixir Daniel drank just before the game begins (which he reads a Note to Self about in the first level) is actually titled "Amnesia", because it is Exactly What It Says On The Bottle. The real purpose of it is to erase the memories of torture victims, so that they forget the specifics of the torture, and leave them to only wonder what caused their scars, their minds constructing fresh horrors anew in anticipation of the next session.
Torture Cellar: Oh God the torture cellar... brass bulls that people are crammed into to be broiled alive, torture wheels that allow for multiple bone breaks - and worst of all, the cells that permit the neighbor to hear nothing but the anguished screams emitting from the torture chambers. Even worse is the reason behind the torturing — see Powered by a Forsaken Child. Almost all of those items are real medieval torture devices that actually existed and were used on people - with the exception of the Iron Maiden, which (despite its many appearances throughout popular culture and inside some historical "tours") is purely fictional as a means of torture. Unfortunately it's only one of many - and the only one that was never used. The others are entirely factual.
Alexander, judging by his notes on the subject. He leaves instructions on how to best inflict prolonged suffering, and deliberately pipes the sound of ongoing torture into the cell areas of the other prisoner awaiting their turn, knowing that the anticipation will only make it worse for them. For all the elaborate devices in the castle, the torture techniques are very primitive, dating back to the Dark Ages. Possibly justified because Alexander is immortal and has been alive for much longer than the era in which the game takes place. However, his torture technique is further backed up by the use a memory-erasing draught called "Amnesia" after each session, just so their imaginations will produce new horrors afresh in anticipation of next time.
Daniel, too, becomes an apprentice of sorts to Alexander as he revels in torturing supposed murderers, arsonists, and rapists.
The Developer Commentarypoints out that the techniques laid out by Alexander are quite similar to the techniques they use to keep the player on edge throughout the experience, making the devs themselves Torture Technicians. Parallel to how the prisoners have to hear their cellmates torture and death, the player is also subjected to auditory hallucinations featuring each of the torture apparatus and their effects before we see them and how they function.
Trauma-Induced Amnesia: Subverted. Daniel induces amnesia on himself willingly, by drinking a certain type of potion. The game starts at the point when he wakes up from his dreamless sleep, now only knowing his name and nothing else.
Überwald: The Prussian woodlands that surround Castle Brennenburg, including the tiny village of Altstadt just down the road. Most of the information on it is revealed through diary entries, notes on the location, and supplemental materials.
Was Once a Man: The creatures hunting Daniel were once soldiers working under Alexander; after giving them tainted wine, BodyHorror ensued, causing them to explode and become horribly misshapen.
Easter Egg: There is a letter from "A.S Laboratories" hidden behind some books on a bookshelf in one of the rooms that mentions a Space-Span Device. A.S Laboratories is the same Aperture Science from the Portal series and the Space-Span device is the portal gun. If you find the letter, at the end in the final room, the body covered in chains and tied to the ceiling is a direct Shout Out to GLaDOS, and the dialogue between Justine and Clarice changes: Justine requests that Clarice post a letter to the mysterious A.S Laboratories to let them know that she is "still alive". The entire set up of the game acts as a Shout Out to Portal.
Even Evil Has Loved Ones: Implied with Justine and Clarice, at least once upon a time. A paper indicates that Justine actually cared enough about Clarice to comfort her when she cried, although it seems that Clarice was actually forbidden from playing with her. Clarice has apparently grown up to be Justine's servant, and she herself seems to be on good terms with Justine, though utterly oblivious to her employer's "games".
Evil Is Easy: Killing the three men is easier than solving the puzzles required to save them. On the other hand, you have to save them in order to get 100% Completion... And the potato.
Eye Scream: A phonograph has some of this. It's also fully voice acted.
And the result of this? That monster trying to kill you.
Hidden Purpose Test: Averted. Justine tells the Player Character that she is in Justine's dungeon at the beginning for Justine's entertainment and to test whether humans will take the easy, selfish way out of a problem or look for a harder way out that does not hurt others. The secret part is that Justine is testing herself.
Meaningful Name Justine's name (Justine Florbelle) is a reference to two works by the Marquis de Sade, Justine and Les Journees de Florbelle. The subtitle of Justine is "The Misfortunes of Virtue" which may apply to the ending, if you get the good ending. Les Journees de Florbelle was destroyed, perhaps reflecting the bad ending and the fact that you can't save the game - if you die, you are destroyed forever and cannot be recovered. Thehorrifying contentofthesenovelsisreflectedinthegameandthecharacter.
Fridge Horror: if the relation to de Sade's work is taken to its logical conclusion, it can be inferred rather too easily that Justine was sexually abused by her father ("Filling the void left by her mother" indeed), and is a corrupt libertine. Just in case you wanted clarification on how evil she is /was
Nothing Is Scarier: Justine doesn't quite follow this... to an extent. There is only one type of monster Justine's former fiancee Alois, and yes, he's still alive and human, a guy named Basile who Justine blinded and calls you profane names, and Malo, who wants to eat you, you encounter each once throughout the expansion, and while looking at Basile drops your sanity, it doesn't always make him more likely to see you... because he's blind. However, he can hear you, and if any of them hits you once, you die, and the game closes, not to mention there are no save points in the expansion whatsoever.
Room Full of Crazy: "The tattered yellow king shall dethrone", "Climb the highest tower, "Oh Father", "The skinless one is waking", "The inside", "Gluttony", "I am emerging", "The beautiful pain", "Lonely", "Through the gates", "It will be the end of everything","What will that perfect sphere bring", "It will be again, It's coming", "From within", "Playful", "Death shall move across the floor", "Spin the wheels crank the engine", "My darlings", "Liar! Alois does to use dust as a sore muse", and who could forget "Suffer the trial" and "Stay alive".
Shoot the Shaggy Dog: Even if you save the hostages, at the end Justine just locks them up in the basement to either starve to death, or to be used again in a later "game".
The Walls Are Closing In: The final challenge room, the player must overcome this. The exposed gears on the wall and various dodads scattered about the floor to jam into them are red herrings to give the player a Hope Spot, though Failure Is the Only Option. There is no way to stop the walls from closing... until they stop on their own.
For good reason, too — the DLC was part of the "Potato Sack" Alternate Reality Game carried on through several indie games, leading up to Portal 2. The backstory for the ARG explains that GLaDOS hijacked all of the games, adding in references to potatoes and so on, and unlocking hints in one game would lead to certain tasks in another in the Sack, all which would unlock clues and actually managed to knock the release time of Portal 2 down by several hours, all by fan cooperation.
Wham Episode: The entire ending. Justine willingly created the monsters from her own friends and lover. The entire story was all a sick "game" she plays purely for her own twisted amusement. And depending on what you did in the final areas, she now has the resources to do it all again.