Adorkable: Jane while she's lying on the examination table in Asgard. She's so delighted by the new tech and asking so many questions that a visibly annoyed Eir has to tell her to be quiet and lie still.
Aerial Canyon Chase: The secret door to other dimensions Loki knows of is hidden in a tiny mountain crevice. He has to pilot the ship through it.
Alien Invasion: Played with. Although the Dark Elves do attack Greenwich, they're not there to conquer Earth, as the Chitauri were in New York. It just so happens that the perfect spot to amplify the Aether with the energy of the Nine Realms is located near Greenwich. This actually makes sense, as in Norse Mythology, Earth is literally the center of World Tree. If you're trying to spread darkness across the cosmos, why not start at literally the heart of the universe?
Even more cleverly, by our own reckoning Greenwich is the center of the Earth, at least with regards to time zones (Greenwich Mean Time).
Aliens Are Bastards: The Dark Elves surely are this for wanting to exterminate all life in the multiverse.
Annoying Younger Sibling: Loki knows how to get under Thor's skin, irritating the heck out of his brother with his shapeshifting pranks and his snarky comments about Thor's piloting skills during their escape from Asgard.
Armor-Piercing Slap: After so many years waiting for him, who said he would return in a short time, Jane received Thor with one of those.
Averted when she tries the same with Loki, only to have it bounce off his arrogance.
When Thor is at Charing Cross Underground station in Central London and asks how to get to Greenwich, the answer he is given — "Three stops on this train" — is impossible. You can get a mainline train to Greenwich from Charing Cross above ground via Waterloo East and London Bridge, but you certainly can't get there in three stops on an Underground train.
When Selvig is being apprehended by police at Stonehenge, a lot of tourists could also be seen in the background pretty much standing right next to the stones. With certain exceptions (summer and winter solstices, spring and autumn equinoxes, special bookings throughout the year), tourists are generally not allowed to even walk near the stones, much less get so close that they could touch them.
Downplayed with Malekith. He's no pushover, but he starts the film physically weaker than his lieutenant Algrim and was taken down by Frigga in one point. He gets much stronger after the power-up with the Aether.
Frigga showing off her swordsmanship is a straight example.
The rank and file Asgardian soldiers drop like flies during the Dark Elf onslaught. Sif and the Warriors three are much better combatants, being higher in the rank structure. Thor, Loki and Odin are nigh invincible for the most part, with Thor and Loki being slightly below a Dark Elf kursed warrior in strength. Plot Armor is obviously at work.
Batman Gambit: Loki and Thor in Svartalfheim. Loki's Reliable Traitor status makes it very convincing for everyone — audience included — when he stabs Thor immediately after having his cuffs removed. Then he chases a tumbling Thor down a hillside, with Jane following, and cuts his hand off halfway through recalling Mjolnir as he calls out Thor on his sentimentality. As Malekith approaches, he grabs Jane and tosses her at them, asking for them to let him watch them destroy Asgard. The moment the Aether is out of Jane, Loki removes the illusion, and Thor blasts the Aether with enough lightning to put a Leviathan down. It doesn't quite work, but the effect was there.
The entire act of bringing Jane to Malekith so he can extract the Aether and Thor can attempt to destroy it is seen as this by Odin, which is why he wants to stare down Malekith in a frontal assault when Malekith comes to claim it in Asgard. Ultimately, while Odin's own plan is patently pyrrhic, he's proven right when Thor does indeed allow Malekith to leave with the Aether once Thor goes against his father's wishes and fails to destroy the Aether when it's pulled from Jane.
Big "NO!": Thor screams "NOOOOO!" when Frigga is slain and another one when Loki seemingly gets killed.
Bittersweet Ending: Thor is able to defeat Malekith and prevent the universe from being destroyed and ends up staying with Jane on Earth. However, he's lost Frigga and his brother, and unbeknownst to him, Loki faked his death and he has usurped the throne from Odin, whose fate isn't revealed.
Black Eyes of Evil: Jane has these several times as a result of being the host of the Aether. When on the Dark World she gains these as well as startlingly blue pupils, not unlike the Dark Elves'. When Malekith absorbs the Aether himself, he temporarily gets black eyes before reverting to red eyes with black pupils.
Black Vikings: In addition to Idris Elba as Heimdall, we can see other Blacks among Asgardian warriors. Also, the Dark Elf Algrim is played by Afro-Brit Adewale Akinnuoye-Agbaje.
Blatant Lies: When Frigga asks, "Am I not your mother?", Loki hesitates for a full five seconds before he unconvincingly replies, "You're not." The sad expression on his face and his reaching out for her hand afterwards prove that he doesn't mean it.
A literal one. When the gang first discover the portals in London, one of them tosses in a brick, and it doesn't come back. Later, when Jane wakes up from being knocked out, the brick is seen in the background appearing out of nowhere and landing.
Later, we find the missing shoes and car keys as well.
At one point a pair of RAF jets fly into one of the other Nine Realms... and at the end of the big battle sequence, they fly out again.
Also, the second stinger shows the Jotunheim beast still running around Greenwich, chasing birds.
Britain Is Only London: Averted. While nearly all of the Earth scenes do take place in Great Britain, it's mentioned that Dr. Selvig had been going around other places in England such as Stonehenge.
The Brute: Kurse is this to Malekith and the entire Dark Elf race.
Upon his return to Earth, Thor tells Jane "I gave you my word I would return", as he promised near the end of Thor.
Loki has been imprisoned as punishment for his actions in The Avengers.
"That was for New York!"
Dr. Selvig's mental state is still a little fragile due to Loki's manipulations, also in The Avengers.
There is a very brief scene in Jotunheim in which we see one of the giant creatures from the previous movie.
At one point, Loki begins taunting Thor by turning into different shapes and eventually takes the form of Captain America.
Odin reminds Loki that if he had not taken him from Jotunheim, he would not be alive today.
A sequence in the Battle of Vanaheim of Mjolnir hitting a Marauder and flying back into Thor's hand mirrors a similar sequence in the Battle on Jotunheim in the first movie.
Jane still has issues with SHIELD.
Darcy still calls Mjolnir "Myeh-myeh".
Volstagg empties his beer and throws the mug on the ground while shouting "Another!", which Thor did in the first movie. Luckily, Volstagg is in Asgard when this happens, so he doesn't get the stares Thor got.
One awesome call back that takes place during the movie; when Thor faces down the rock monster, he tells it, "I accept your surrender." before smashing it into pieces. He later tells Malekith the same thing before defeating him.
Heimdall is the only one aware that Loki has knowledge of secret doorways out of Asgard. In Thor, Loki revealed this to Heimdall just before freezing him with the Casket of Ancient Winters.
When Thor is holding council with Heimdall, Sif, and the Warriors Three (well, two of them), Volstagg mentions that the Tesseract is under heavy security - at the same time confirming it can still be used for travel between worlds a la Bifröst.
Loki stabbing Thor on Svartalfheim mirrors a similar scene in The Avengers.
Loki introduces himself to Malekith as "Loki of Jotunheim". This is a call back to both Thor, where his Jotun origin was revealed, and The Avengers, where he introduced himself as "Loki of Asgard".
One of Loki's last lines in Thor is to Odin, after his failed attempt to destroy Jotunheim: "I did it for you, father!" Fast forward two movies, when Loki is "dying" after saving Thor from the Kursed, Thor says that he will tell Odin of what he did, to which Loki replies "I didn't do it for him," showing how much Loki has changed since the first film.
When Thor offers to return his hammer to Odin, Odin refuses it because "Odin" is really Loki, and Loki knows from the previous film that he wouldn't be able lift the hammer.
The Cameo: As Loki considers some disguises, he tries out Captain America. Tom Hiddleston wore a Cap suit and did an impression of him while staying in character as Loki, and Chris Evans' performance was based on that.
Captain Obvious: Loki, telling Thor that the other ships are firing at them.
Car Fu: In the climax, Ian uses a car that has been rendered weightless (but not massless) by the convergence to crush a pack of Dark Elves.
Casual Danger Dialog: Happens at least once between Thor and Sif, with her commenting that everything was under control and him asking with a grin if that was the reason everything was on fire. Plus:
(a Kronan enters the fray as the Marauders cheer on) Sif: All yours.
The Chains of Commanding/Reluctant Ruler: Discussed during the denouement of the film between Thor and Odin: with Thor witnessing how the challenges Odin were facing for the rest of the film have taken their toll on him (see Not So Different below), Thor seems to have decided to not succeed as Asgard's king, but promises to be an independent protector of the Nine Realms. Which Odin seems to have peacefully accepted, if only because he's actually Loki in disguise, having usurped the throne.
Chekhov's Gag: Ian losing the car keys by tossing them in the portal and finding that not everything thrown there comes back is funny - and comes back later when Jane finds the keys in the dark world, showing her where the portal is. Turns into a Chekhov's Gun when she uses them to drive the car they had left behind in order to get to Greenwich.
Frigga is a master of illusion, who taught Loki most of what he knows in that regard. She uses these abilities to first visit Loki in his cell, then later to hide Jane.
Loki's shapeshifting, which is Played for Laughs during the escape from Asgard. He uses the ability to create illusions and project illusions over others to persuade Malekith to draw the Aether out of Jane. Later, he uses these abilities to infiltrate Asgard and usurp the throne in the guise of Odin, even using the same guard disguise.
Clingy MacGuffin: Jane unwittingly becomes the host to the Aether, a shapeless mass of energy, and part of the movie is trying to remove it from her while it serves as the MacGuffin for Malekith, who wants to use it for his own reasons.
Coincidental Broadcast: While Darcy tries to get into contact with Erik Selvig, a news report comes on the television revealing where he is: locked up in a mental ward for running around Stonehenge completely naked. Somewhat subverted by the fact that it's a repeat of the news story reported earlier when Jane provides exposition about his mental breakdown and mentions not being able to contact him earlier.
Colony Drop: As a last ditch attempt to defeat Bor's forces, Malekith disables all of the Dark Elf ships hovering above Svartalfheim and tries to drop them on the soldiers.
Cool Versus Awesome: The movie can best be summed up as alien elves in starships vs. space vikings in flying longboats with lasers.
Could Say It But: At the end, Thor refuses the throne, believing himself a better guardian if given the freedom to come and go as he pleases. Odin insists that he cannot personally condone Thor's actions, nor can he tell his son how proud he is of him for doing so. Subverted in that it's not really Odin...
The Cuckoolander Was Right: Dr. Selvig is placed in a mental ward, but his theories about the Convergence are actually true. He also had legitimate mental problems that justified putting him in a hospital. However, when he realizes he was right all along, he tosses the enormous bag of meds he's been prescribed.
Frigga defeats Malekith with ease, in a dress, with only one arm. When Kurse shows up, things go in quite the other direction.
For the bad guys, the Dark Elves overrun Asgard's defenses thanks to Kurse sabotaging them, and the only reason they retreat is because Malekith was injured by Thor.
Kurse starts off giving one of these to Thor, pummelling his face into the ground and throwing boulders at him.
Darker and Edgier: The color scheme alone is a lot grimmer, there's a full-scale war, and Thor claims this time he's ready to kill Loki if his genocidal sibling steps out of line. Hell, even the title reflects this. On the other hand, there's still a lot of humor, and much of the final battle is a mix of humor and action.
Dark Is Evil: The "Dark Elves" are the antagonists of this film.
Deflector Shields: Asgard's main citadel is defended with one. Although it doesn't take long for Algrim to take out the main engine and disable it.
Demoted to Extra: Hogun the Grim's role is reduced to two brief scenes from the already sparse screentime he had in the prior film, having decided to stay in Vanaheim. In contrast, the rest of the Asgardians receive expanded roles.
Derelict Graveyard: Svartalfheim is full of wrecked spaceships, a relic of the Dark Elf - Asgard war millennia ago.
Destructive Savior: Sure, Thor intends to save Asgard from Malekith's impending invasion - but he's caused a lot of property damage in the realm during his dashing, "treasonous" escape from Odin's pursuit, including (but not limited to) the humongous monument of his grandfather Bor, King of Asgard before Odin himself.
Disturbed Doves: Starlings are disturbed and flying in an erratic manner just before the elves invade Earth.
Double Meaning: When an Einherjar "soldier" comes to report Loki's death to Odin, the Allfather looks distressed and says, "Loki!" The in-universe explanation is Odin is upset over the loss of his son, but it's also a hint to the audience, since the soldier is Loki!
Loki: I thought you said you knew how to fly this. Thor: I said, "How hard could it be?" Loki:(several crashes later) I think you missed a column. Thor: Shut up.
Dungeon Bypass: Instead of a long, prolonged battle with Malekith's army to get the Aether, Bor elects to just teleport the Aether back to Asgard with the Bifrost before the war even ends.
Early-Bird Cameo: The Collector, from the upcoming Guardians of the Galaxy film, shows up in the mid-credits Stinger.
Eldritch Starship: The Dark Elf spaceships resemble floating towers or skyscrapers, menacingly glow with red lights, and generally look otherworldly and unsettling.
Elves VS Dwarves: Played with. While they don't exactly match the respective archetypes, armies of Svartalfheim and Asgard fit the general aesthetics of the conflict (somewhat ironically there was little difference between the Svartalfar and Dwarfs in Norse Mythology).
Even Bad Men Love Their Mamas: The one time Loki shows any true, sincere emotion in the film was in the solitude of his cell, without any witnesses as he smashes the furniture around him in grief at the news of Frigga's death. Later, when Thor asks him to dispel the illusion, he hasn't bothered to clean it up at all, and appears notably unkempt. In his first scene, Loki puts on a contemptuous façade, but his mask slips when Odin informs him that he will never see Frigga again; he then stumbles as he's being led away by the guards.
Evil Is Petty: During the attack on Asgard, Malekith takes the time to destroy Odin's throne.
Evil Overlooker: Malekith in one of the posters and when he witnesses his fellow Dark Elves awakening.
Final Solution: Bor's answer to the constant threat of the Dark Elves, which Odin grinned about when recounting. Justified in the Dark Elves were constantly trying to destroy all life in the multiverse. Ironically, Malekeith contributed his own fair share to this to cover his escape.
Fish out of Water: Last time, Thor struggled to adjust to the world of Earth with Jane as his guide. Now the roles are reversed and it's Jane's turn to adjust to the other worlds of the Nine Realms. Surprisingly, she's quite comfortable with it.
Force-Field Door: Asgardian prisons utilize this technology. A similar technology is used as Deflector Shields which cover the main Asgardian citadel. Predictably, they both fall to Kurse.
Foreshadowing: Loki briefly impersonates an Einherjar warrior during his and Thor's escape from prison. Loki later impersonates such a warrior, possibly the same one, after his apparent "death" in order to sneak back into Asgard. There's also a telltale green glow during the second instance.
In the same instance, the transformation of Thor into Sif shows that he's able to project illusions/shapes onto other people, thus making the Batman Gambit possible.
Full-Name Basis: Asgardians almost exclusively address Thor's girlfriend as "Jane Foster", seemingly unfamiliar with Midgardian given names and surnames.
Gainaxing: Jane gets some rather prominent slow-motion jiggle in the library near the climax.
Gender Bender: Temporarily done to Thor by Loki as they are escaping from Asgard, transforming him into Sif as a joke.
Generic Doomsday Villain: Malekith the Accursed is out to destroy the universe and return everything to darkness. Why? Because. He's less a character and more a plot device to justify having Thor and Loki team up.
Becomes a Running Gag when all of Thor's friends in Asgard tell Loki the same.
Loki: Evidently, there will be a line.
Genre Shift: With the introduction of Dark Elves, and increased screen time for Asgard, the film drifts towards Science Fantasy in terms of look and feel. At times it verges on Space Opera, with battles between ships and gun batteries full of laser fire and holographic interfaces, and much more travel to other worlds.
Gilded Cage: Thanks to Frigga intervening on his behalf, Loki's prison cell has fairly lavish furniture and looks very comfortable — but it's just as confined as the others.
A God I Am Not: When Loki tries to claim that he merely intended to rule Earth as a benevolent god, Odin counters that they're no more gods than Earthlings are. Loki counter-counters that they live a whole lot longer.
Loki: You must be truly desperate to come to me for help.
Gravity Screw: The effect of the nine realms aligning themselves. Some things float, some bounce between different points or pop up in unexpected places. This is explained as the borders of the realms blurring.
Heel-Face Revolving Door: Unsurprisingly, Loki. He switches between a staged betrayal of Thor in front of Malekith to him protecting Jane and seemingly sacrificing himself for Thor to usurping the throne from Odin behind Thor's back.
Helmets Are Hardly Heroic: Once again, Thor, Sif, nor any of the Warriors Three wear a helmet, and Loki notably never wears his enormous horned helmet from the previous movies where he was the main villain.
Loki pushes Jane out of a grenade's path and nearly dies before Thor saves him. Later, he takes out Kurse at what seems to be the cost of his own life... and then subverted when it turns out he's Faking the Dead.
Frigga refuses to reveal Jane Foster's location, even when threatened with certain death. She's murdered for her efforts.
Hoist by His Own Petard: Algrim is annihilated by a black hole grenade, a weapon of the Dark Elves, that was activated by Loki. Malekith is crushed by his own Eldritch Starship teleported to him by Selvig.
Hypocritical Humor: Loki tells Thor he can't solve all his problems by hitting things. This from a guy who's twice tried to fix his self-image problems by destroying planets.
I Choose to Stay: Thor abdicates from his duties to the throne of Asgard to protect the Nine Realms and live on Earth with Jane.
I Have No Son: Odin makes it pretty clear that he no longer considers Loki his son and would've have had him executed if weren't for Frigga.
I'm Not Hungry: Jane Foster says this word for word while rejecting a meal brought by a guard. It turns out it wasn't a guard at all but Lady Sif in disguise, pretending to bring Jane food in order to rescue her.
"I Know What We Can Do" Cut: When Thor decides to go after Malekith, which requires overcoming numerous obstacles starting with the fact that Odin has forbidden him to leave Asgard, the ensuing sequence alternates between Thor explaining his plan to his friends and the plan being carried out.
Irony: After Frigga dies, Odin wants to face the Dark Elves on a martial basis, while Thor is proposing a more peaceful solution. This is the exact reverse of their positions at the start of the first film.
It's Personal: Malekith killing Frigga is this for the Asgardian royal family. Even Loki, for all his posturing, is wounded by the news and agrees to assist Thor's campaign of treason in order to get at Malekith. He even tells Thor to "trust his rage" even if Thor cannot trust the man himself, certifying how his desire for vengeance overrides any other element of his personality.
Jacob and Esau: It seems that Loki was his mother's favourite, while Thor was his father's.
Last Of Their Kind: Malekith and his ship's inhabitants are all that remain of the Dark Elves. By the end, it's safe to say that they've been wiped out altogether. Algrim is the final Kursed, be it a lost art/technology or it has some further significance to Malekith.
Legacy Character: The Kurse powerset and name is given to dark elves if they've proven worthy in the eyes of Malekith. Algrim is such an elf.
Leitmotif: Hilariously, Steve's turns up when Loki turns into Captain America and proceeds to mock him mercilessly. This makes it the first theme to appear in three MCU movie series, as it also makes a cameo in The Avengers.
The Living Dead: As Thor cradles Frigga's body after she was slain by Algrim, you can see her breathing (accentuated by her belt pouches moving up and down).
Logo Joke: In the trailer, the red background in the Marvel logo moves to show Thor's cape.
Long Lived: It turns out that Asgardians aren't actually immortal gods, according to Odin. They're born, live for at least five thousand years according to Loki, and eventually die. This has some basis in Norse Mythology, as the Aesir were established as capable of dying (in fact, Ragnarok has a pretty detailed list on how some of them will die). The only way the Aesir were able to retain youth was from eating Idunn's apples; since the MCU has Adapted Out these, it stands that the Asgardians would eventually succumb to old age.
Loophole Abuse: Heimdall is bound to report any knowledge of treason to Odin. So he summons Odin and the guards to Bifrost to inform them that he's committing treason, which he is - by failing to report the treason also being carried out at that very minute all the way back at the palace.
Frigga, on the other hand, has never shown anything except respect, amicability and concern for Jane, even going to the extent of protecting her with her life from Malekith, although whether that's really for her or for the Aether possessing her is muddy.
Luxury Prison Suite: Loki's cell is lavishly furnished and quite comfortable, but as confined as the others. Justified, as his mother mentions bringing him books. It can be assumed she tried to make him comfortable, too.
Magic Versus Science: A downplayed version with both sides using Magitek. The Dark Elves focus more on beam weapons and artificial black hole grenades, using space ships to travel, but beef up their elite troops with magic. Asgardians focus on using close combat pre-industry weapons and travel by the Bifrost, but have beam batteries and Viking-vessels for defense.
Magitek: As always, the line between the Asgardian's magic and their technology is so blurry they don't bother to make the distinction. Jane is actually able to identify the medical device they put her in. They call it a soul forge, she calls it a quantum field generator.
Mineral MacGuffin: Averted. Odin notes that most objects of power are gems, but the Aether is a fluid.
Misfit Mobilization Moment: The final battle has all of the human characters, all of whom are varying degrees of quirky, band together with Thor and remind the viewers that they're also brilliant scientists (and that Thor is a tactician as well, if a boisterous one) - pushing back the invading forces and executing a plan that ultimately defeats Malekith with science when brute force failed.
A somber Viking Funeral scene is followed by Dr. Selvig's insane lecture in a mental ward.
Malekith manages to bring Thor down with the Aether and tries to pummel him. Cue them teleporting above London's St. Mary Axe (Also known as the "Gherkin") , cracking it and sliding down the windows with onlookers just watching them fall. In addition to this, following a few more random moments of warping that see Thor struggling to summon Mjolnir back to his hand, Thor ends up in a London Underground station. He quickly asks a bystander how to get back to Greenwich. She says by taking the train she's on for three stops, which Thor responds to by calmly boarding the train and commuting back to the battle.
Not long after Thor is mourning Loki's supposed sacrifice, Jane's phone rings with a rap ringtone.
After being reunited with Thor, Dr. Selvig asks (very nervously) about Loki's whereabouts. Thor somberly delivers the news of Loki's apparent death, to which Selvig cheerily replies, "Oh thank god!" To Selvig's credit, he quickly catches himself and offers his condolences after seeing Thor's reaction.
Mordor: Svartalfheim is a bleak, ash-covered wasteland.
Mr. Fanservice: Thor, naturally. There's even a hilarious blatant pair of shots devoted to his magnificent chest and equally glorious back, both glistening with water from a sponge bath.
Thor's latest costume is inspired by his 1980s comic book incarnation; the same era that introduced Malekith.
Thor hammers a Kronan (or a Stone Man From Saturn as they were dubbed back in the Silver Age, where they served as the first ever villains Thor fought).
Malekith seeks Jane for his own purposes. He used Sif in a similar manner in his first appearance.
Odin gives a nod to the actual Norse mythology when he states a goat doesn't belong on a banquet table.
Malekith getting half his face burnt makes him look more like the comic book Malekith, whose face was half white and half black.
During Selvig's rambling lecture about the Convergence, a circled "616 universe" can be seen in the center of the blackboard. This refers to Marvel's designation for the mainstream comic continuity.
Malekith and Kurse had first appeared in comics at The Surtur Saga. There's a point of that story adapted into the film as well: Loki seems to betray the Asgardians for Malekith, but he was actually a Reverse Mole all the time.
Odin suggests that Thor should forget Jane Foster and focus on what's "in front of him", while the two are looking at Sif training for battle. Besides the obvious point (Odin would prefer Thor to be with Sif instead of Jane), this could be a subtle nod to the comics, where Thor's romantic relationship with Jane ended a long time ago, and after that he's had an on-again, off-again relationship with Sif for years. (Note also that in the actual Norse myths, Sif is Thor's wife.)
Naked People Are Funny: Erik Selvig runs around Stonehenge while doing his research in his birthday suit due to the insanity he gained from being mind controlled in The Avengers.
Never Bring a Knife to a Gun Fight: Asgard's troops are initially outmatched when the Dark Elves first breech Odin's palace when the shield is lowered, as the Dark Elves carry laser rifles and Asgard's soldiers are only armed with swords and shields, causing a fair number to get shot as the Elves pour out of their craft. However, once the Asgardian forces can get within melee range the battle becomes more contentious.
Back in full force with Loki's character. From his conversation with the Frigga illusion she conjured to visit him to a conversation with Thor in Svartalfheim, he constantly says that he did nothing to deserve his punishment.
Loki: Who put me there?! WHO PUT ME THERE?! Thor: (grabbing Loki by the throat and slamming him against the side of the boat) You know damn well! YOU KNOW DAMN WELL WHO!
Malekith blames Asgard for the Colony Drop he himself ordered that annihilated his own people.
The trailer has Loki commenting, "Hitting doesn't solve everything, brother," while Thor takes down a troll. In the theatrical cut Loki is nowhere near Vanaheim during the time of the battle.
During the trailer, the dialog between Thor and Heimdall discussing Loki implies that Loki has had dealings with the Dark Elves. In actual movie nobody has interacted with the Dark Elves for thousands of years. What Loki knew was the secret portals that can be used exit Asgard.
The trailer also removes all of Loki's broken furniture, hiding his breakdown after Frigga's death.
The trailers suggested that there would be a Love Triangle between Thor, Sif, and Jane. This plot amounts to a single conversation between Odin and Thor, and a slight bit of tension between Jane and Sif that doesn't have an influence on the story.
Malekith's invasion of Greenwich appears in the beginning of most trailers, implying this is the start of the story as well. In fact, it's the last act of the movie.
The scene where Thor recruits Loki was altered for the trailers: In the trailer Thor says, "You should know that when you betray me, I will kill you," while in the movie Thor makes a short speech saying that while he may have retained some hope of redeeming Loki in the past, he doesn't anymore, and that if Loki betrays him Thor won't hesitate to kill Loki.
In trailers, the scene where Thor and Loki are walking together down a hall was edited to look like a Bad AssPower Walk, with fans thinking the scene would be a Crowning Moment of Awesome the first time the trailer was shown. In the movie, it is a very humorous scene, with Loki teasing Thor the whole way.
Nice Job Breaking It, Hero: A twofer. If Odin had listened to Thor when he argued that their best course of action was to take Jane off Asgard so Malekith wouldn't target them a second time in order to get the Aether, Thor wouldn't have sprung Loki from his cell and subsequently the actions that led to Loki usurping the throne of Asgard would not have come to pass.
And in the stinger apparently the Asgardians aren't Genre Savvy enough to avoid giving one of a set of Infinity Stones to a guy called "The Collector".
Then there's Thor's plan: instead of staying at the heavily fortified Asgard, with literally an army at his beck and call, Thor heads to the Dark World with Loki and Jane, who's carrying the Aether, the superweapon needed for the Big Bad to destroy the universe, then tries to destroy it as Malekith draws it out of Jane. The result? Thor fails completely and all but literally hands over the Aether to Malekith on a silver platter. This at least manages to save Jane's life.
Loki's not exactly a hero, but if he hadn't told Kurse which staircase to take out of the prison, the Dark Elf might not have been able to bring down Asgard's defensive shield to let Malekith in... and Frigga might not have died.
Nobody Poops: The prison cells on Asgard, holding prisoners from across the worlds and realms, are all constantly sparkling-clean and white-walled/floored with no evidence whatsoever of being equipped with toilets/latrines during the scenes where they appear.
No, Except Yes: In the first scene, before Loki is led to prison, he speaks with Odin.
Loki: It's not that I don't love our chats... It's just... I don't love them.
No Man of Woman Born: Kurse is told that no power the Dark Elves' enemies possess will be able to harm him. True enough, he's killed using his own weapon.
No Medication for Me: After being sprung from the Asylum, Selvig throws away his big bag of prescription medicine. In his case, it seems that the medication was either genuinely unneeded or reacted badly with him, because he spends the rest of the movie far more stable, if still a bit strange.
Nonchalant Dodge: During the Portal Cut moment with the police car, Heimdall leans to the side a bit so the bumper just sails past him harmlessly.
Not Me This Time: Thor's first thought when he hears rioting in the prison is, "Loki." Actually, he's about the only prisoner not involved in the riot started by Algrim.
During Odin and Loki's first scene together, Loki points out that his actions in leading armies to subdue and conquer the other realms is Not So Different from Odin (and Bor's) own war-torn history. Odin doesn't really address this, except by denying that Loki was ever in line for the Asgardian throne and thus has no birthright.
A subtler example is how Thor and Loki have influenced each other's abilities and mannerisms. Thor has learned some trickery and sarcasm from his adopted brother, while Loki has become a braver and stronger melee fighter.
Out-of-Character Alert: When it looks like Loki's betraying Thor, he introduces himself to Malekith as "Loki of Jotunheim". Anyone who recalls the first film will know that Loki hates his true parentage, therefore cluing us in that something is amiss. There was; the betrayal was a ruse to get the Aether out of Jane so that it could be destroyed.
OOC Is Serious Business: Loki destroying his cell's furniture in solitude when after he is informed that his mother is dead. This is an indicator to the audience that despite Loki's Chronic Backstabbing Disorder and otherwise collected and manipulative personality, his desire to see Malekith pay for what he has done and alignment with Thor if he must is unshakable ("trust my rage"), even if it would appear otherwise...
Personal Raincloud: Inverted. The first clue that Jane and Darcy have that Thor's back on Earth is that they're in a rainstorm but inexplicably in the middle of a dry circle. Then Jane sees and runs over to Thor and the circle follows her, leaving Darcy soaked.
Pet the Dog: During the battle against Malekith and the Dark Elves, Kurse throws a black hole grenade at Loki and Jane. Loki pushes Jane aside without thinking and almost dies as a result. Possibly subverted, as he may have done so to gain Thor's trust to set his own plan in motion, faking his death and usurping the throne of Asgard disguised as Odin. Although if that were true, it would be quite a gamble on his part.
Pietŕ Plagiarism: Loki is the recipient of this when Thor cradles him in his arms after he is stabbed by Kurse.
Portal Cut: When Thor takes Jane to Asgard, the Bifrost clips the front end of a nearby police car. The bumper tumbles out the other end a few seconds before Thor and Jane arrive. Later on, Malekith loses a couple of limbs to Selvig's gravitational spikes, which have been reconfigured to open rifts.
Prison Riot: Algrim, posing as one of the captured marauders, starts one in the dungeons of Asgard as a part of Dark Elves' plan to attack the place and collect the Aether from Jane.
Put on a Bus: Hogun leaves Asgard for Vanaheim, though he has a brief cameo later.
Pyrrhic Victory: Odin, stricken with grief over his wife's murder, is willing to "win" such a victory by allowing the Dark Elves to invade Asgard. Thor tries to point out that this is crazy and a reckless waste of his people's lives, but Odin's fury blinds him to it.
Recruiting The Criminal: Thor enlists Loki's help due to his ability to find ways out of Asgard no one else is aware of.
Recycled Premise: The introduction. A long time ago, the dark lord Malekith has a terrible weapon, the Aether, and sought to destroy the universe with it and fill it with darkness. But there were some who resisted. A last alliance of warriors from all realms marched against the armies of dark elves. And there, on the slopes of Svartalfheim, they fought for the freedom of the nine worlds. It was in their darkest moment, when all hope had faded, that Bor, father of Odin, took up his realm's mightiest weapon. Malekith, the enemy of the free peoples of the Nine Worlds, was defeated. But the power of the Aether could not be undone. It was hidden, and kept away from all living beings. Malekith survived, to be awaked when the Aether was picked up by the most unlikely creature imaginable - a human, Jane Foster of Midgard. Sounds familiar?
Red Right Hand: Malekith is disfigured on one side of his face thanks to a blast of lightning from Mjolnir.
Red Shirt Army: The Einherjar are dedicated enough but still mostly helpless against the more technologically advanced Dark Elves. Averted in the prologue, where the Einherjar under Odin's father Bor eventually overcome the Dark Elves. It probably helps that they were mobilized for an invasion, as opposed to being caught flat-footed on their own soil.
Rescue Romance: Played for laughs. After Ian saves Darcy from some Dark Elves, she dips him and plants one on him.
Revenge: After Frigga is murdered, this becomes Loki's motivation to team up with Thor to stop Malekith.
Revenge Before Reason: Odin slips into this after Frigga's death, with Thor pointing out that he's no better than Malekith if he's willing to throw away the lives of his own people in the name of victory.
Roaring Rampage of Revenge: Loki's motivation for working with Thor and tracking down Malekith. Thor does it for the sake of averting a bloody conflict with the Dark Elves but Loki doing so is purely to see Malekith suffer.
It doesn't matter much since this is a comic book adaption, but in Norse Mythology, "Svartálfar" (Dark Elves) are actually dwarves. In the comic books, they're still elves. In the original texts this sort of flip-flops, with dark elves sometimes being the same as dwarves and other times a separate race.
The Einherjar, in both the Norse myths and the Marvel comics, are the souls of the glorious dead feasting in Valhalla. In here, they are Asgard's city guards.
Odin's rebuttal to Loki's claim of godhood is that Asgardians are mortal (albeit long-lived). Just like they are in the actual mythology (wherein they are gods).
See You In Hel: Loki says this to Kurse right before killing him, while seemingly mortally wounded himself.Fridge Brilliance in that not only does Hel actually come from Norse Mythology, but in the original myths, she's Loki's daughter.
Sequel Escalation: In Thor and The Avengers, only one of the Nine Realms came under threat. In this film, Malekith threatens to erase light from the all the universe.
Sequel Goes Foreign: The first film took place in New Mexico. This one, all scenes in Earth are in London.
A mid-credits scene has Sif and Volstagg giving the remains of the Aether to the Collector for safekeeping in his vaults. The two Asgardians mention both the Aether and the Tesseract being Infinity Stones, and not wanting them near each other. The Collector takes the Aether and, after the two depart, smirks and says, "One down, five to go."
The post-credits scene has Thor reunite with Jane back on Earth, then shows the Jotunheim beast in London chasing some pigeons.
Staring Down Cthulhu: Loki does this to Kurse during the Prison Riot when Kurse walks by his cell, wondering if he'll break him out. Kurse seems to consider, but to him, Loki apparently didn't look useful.
Super Cell Reception: Jane gets a signal in the cave on Svartalfheim where all the stuff that teleported in the beginning of the movie ended up. It helps her find a rift back to Earth after she and Thor have been stranded there.
Teleport Spam: An uncontrolled version: in the final battle, the convergence has turned reality into swiss cheese, so Thor and Malekith (and various other things) end up teleporting between the realms constantly during their slugfest. For added trouble, Thor's attempts to recall his hammer keep failing because they keep ending up in different realms.
While they don't go full Xena, Jane and Darcy are much more proactive in this movie and make a major contribution in the final battle.
Loki is a much more effective melee fighter in this movie than in his previous appearances; here he was armed with only a simple dagger and took on several foes at the same time. In the past, he relied on throwing magical "knives" from a distance, his illusion spell, or a powerful scepter, and he usually focused on one enemy at a time.
Touch of Death: By grabbing the necks of his enemies, Kurse can superheat his enemies to smoldering corpses.
Trend Covers: Compare the poster of this movie to that of Iron Man 3. Both feature the eponymous heroes clutching their respective lady friends in the center, with their foes overlooking them, and their allies off to the sides.
Trojan Prisoner: Algrim lets himself be captured and imprisoned in Asgard so that he can undermine its defences from within.
Vanity Plate: A new one for Marvel Studios along with a fanfare (by this film's composer Brian Tyler) debuts in this film.
Loki shows uncharacteristic bravery and willingness to put his life on the line for others during his team-up with Thor.
Algrim is unquestioningly loyal to his master and offers to sacrifice himself if it helps to advance his Evil Plan.
Voluntary Shapeshifting: One of Loki's powers. When Thor busts him out of his cell, Loki suggests several disguises, transforming himself into an Asgardian soldier, turning Thor into Sif(while retaining his voice), and transforming himself into Captain America. Later, near the end of the film, Loki is revealed to have taken Odin's form after faking his own death.
Vitriolic Best Buds: While not the best of friends anymore, Thor and Loki still act like this regardless, trading insults with each other. May cross with Friendly Enemy to some degree.
World Gone Mad: As the Convergence begins forming rifts everywhere, a flock of birds fly into a portal then exit by flying up right in front of Selvig, Ian, and Darcy. Selvig merely comments:
Selvig: Nothing more reassuring than to know that the world is crazier than you are.
World of Badass: Asgard, Svartalfheim and Vanaheim are full of great warriors. And Earth has the scientists who end up defeating the Big Bad.
The Wrongful Heir to the Throne: In his first film, Thor was unready to be king because he was too immature. In this film, he's matured to realize that he doesn't want to be king because he finds the sacrifices and ruthlessness required to be distasteful. Loki, on the other hand... When he claims that he was far better suited to be king than Thor, Odin doesn't disagree.
Year Outside, Hour Inside: For Jane, it was quick, but when she was teleported to another dimension and back, she had been missing for 5 hours. Possibly subverted, since Jane was knocked out when the Aether entered her body and she could have simply been unconscious.
You're Insane!: Thor's reaction when Loki reveals his secret passage way out of Asgard, which involves driving a ship at high speeds through a crevice.
You're Not My Father: Loki furiously yells a variation of this when he and Frigga discuss Odin. Somewhat justified, as Loki had been disowned and would've been executed if it weren't for his mother's influence.