Kick the Son of a Bitch: It's basic background for the setting that Sparks are hated, shunned and often violently attacked in places where they don't rule. Given that their "gift" endows them with both an obliviousness to contemplating the negative possibilities of an experiment instead of just doing it For Science! and a case of Moral Myopia that leads to them regarding all other humans as nothing but fodder for and/or components in experiments, it's hard to feel too upset about the fact many normals want to get rid of them... until you consider that the self-controlled ones that avoid making offensive/destructive things are the ones most vulnerable to the lynch mobs.
Klatchian Coffee: Agatha discovers coffee in a Mechanicsburg coffeehouse and goes sparky. She also goes into Bullet Time — reading a book on coffee, editing it, and devising a way to rebuild the coffee machine in the time it takes a waitress to say three words.
Knee-capping: Higgs uses this move against Zola. Unfortunately for him, she is too high on combat drugs to fall down.
Laser-Guided Karma: An officer in one of the many armies that invade Mechanicsburg tells his soldiers not to take their eyes off the captured civilians, to treat them with respect, and to execute them all. Right before the Doom bell knocks all the soldiers out.
Civilian man: And what about the one giving orders? Civilian woman: (holding a rolling pin) Oh, him we treat with respect.
Leitmotif / Theme Music Powerup: Agatha discovers that if she hums a certain series of notes, she can improve her focus while working on various projects. This tune pops up throughout the series, in various forms. Unknown if anyone has actually tabulated and played her song in real life, though.
After the Time Skip, Gil's new rather tall and imposing female-figure bodyguard clank "Bohrlaika", is quite nimble, packs an electo-sword that can cleanly cut off an arm off an enemy Humongous Mecha war clank, and was no worse for wear after missing the fact that the arm was about to fall on her when she was reiterating her surrender demand.
Lingerie Scene: The creators admit the work contains "lots of running around in Victorian underwear". Most of the time, Agatha is the offender. Not that surprising, when one of the creators is a big fan of such underthings, and the other is her husband.
Gil: Well, when I was a kid, we heard some of the older guys talking, but we were kind of... um... unclear on the concept, and, well... Zoing: Itworkz! itworkz! DuPree: That is so just like you... soooo pathetic.
Literary Agent Hypothesis: The entire comic is postulated as a course on the life of Agatha Heterodyne, as taught by the Professors Foglio at Transylvania Polygnostic University ("Know enough to be afraid.") They stick mostly to the truth — though this very admittance means that it's possible that, in the "real" universe where this story takes place, not every woman has large breasts.
That is, the first print collection, "Agatha Heterodyne & The Beetleburg Clank", and the original printed comics, are presented as an unauthorized but accurate record published by TPU, Phil Foglio having witnessed Agatha's "Battle Circus" himself; later, he is indeed in town when the Battle Circus episode occurs. However, Phil Foglio is also shown telling the tale as fiction in the street right on page one. (An alternative tryout sketch released online seems to have Agatha herself telling the story to her grandchildren.) Maybe that's after he was accidentally sent back in time or something. But also, in the "radio play" episodes of the webcomic, Studio Foglio are repeatedly shown escaping as they perform the last seconds of the episode just as the real and angry Agatha Heterodyne and her friends are about to catch them and stop the show.
Loads and Loads of Characters: There really are a lot of regular characters in this comic, to the point where it can get difficult to keep track of everyone.
Long-Haired Pretty Boy: Maxim, the beautiful male Jägermonster. See the Cinderella breather episode, where Maxim is supposed to be one of the "ugly" stepsisters, but it doesn't quite turn out as planned.
Agatha, Gil, and Tarvek. The existence of the triangle has now been openly stated, and Agatha's subjects are taking bets over who's going to win (Or if she'll choose both). There was also a low-grade one involving Lars, but Death of the Hypotenuse made sure that only Gil and Tarvek remained to vie for her affection.
Zola: Avoid any floorstone marked in white. It is a trap that will kill you. Do not stand under any part of the ceiling marked in white. It is a trap that will kill you. Duck under any opening taller than one meter. It is a trap that will kill you. Do not touch any metal surface. It is a trap that will kill you.
Zola: This place is dangerous, twisted, and worst of all— [...] It likes to think it has a sense of humor.
Mama Bear: Von Pinn, and how. She's actually the Muse of protection, downloaded into a construct body. The "bear" part gets much more literal later on.
Word of God has it that Theopholous DuMedd was originally "doomed" to be killed off in volume 3, but the Foglios so enjoyed him that he stuck around.
Most likely Sleipnir O'Hara wasn't supposed to be kept around either. Agatha needed a roommate to introduce her to the world of the Baron's flying castle, so the Foglios gave her someone to "sleep near".
The town of Mechanicsburg is integrated with the mechanical Castle Heterodyne.
Bangladesh DuPree. Bang duPrey. Or Du-praved.
Heterodyne: The principle of periodic functions upon which theremins and radio modulation rely. Possibly related to the Theme Music Power-Up.
Othar Tryggvassen, GENTLEMAN ADVENTURER. His surname roughly means "Safe Waters" in the North Countries where he's said to be from.
Doctor Chouteh (pronounced shout-ay) is a Large Ham of ridiculous proportions.
Agatha's foster parents are called Adam and Lilith and it doesn't look like they are very god-fearing. Not to mention their surname, Clay.
Mechanical Evolution: Inverted; Agatha tends to compulsively construct little Clanks termed "dingbots". These dingbots can then go on to construct more dingbots, but dingbots are only so bright, so each successive generation gets less and less advanced, and less bright, and by the third or fourth generation the dingbots produced are nonfunctional.
Gilgamesh and Agatha while testing Gil's flying, or rather falling, machine. Of course because they're sparks, it starts to become midair redesigning the device before Zoing points out to Agatha that they are still falling.
Tarvek is forced to do the same thing... while tied up to a Spark fighting with a mad Jäger on board. He finally makes the machine fly inches from the ground.
There's been strong fan support for Violetta×Von Zinzer, minions in denial and retainer/NOT-minion of Tarvek and Agatha, respectively. Shipping a snarkyMcNinja who hates her job with a world-weary ex-soldier just works.
Mistaken for Quake: when Agatha finally manages to reboot Castle Heterodyne, the invading forces think they're experiencing an earthquake until they discover that it's actually the castle fighting back, seen here.
Modesty Towel: Agatha actually invokes the trope while on the Corbettite Railways, using it as a ploy to distract anybody entering her compartiment, giving time for Krosp (and later Wooster) to take them out if they happen to be hostile. Unluckily, all those coming to visit are either allies or just train attendants, and thus she gives each of them an eyeful for nothing. She has pretty much given up on the pretense when an actual assassin shows up.
Must Have Caffeine: Vanamonde von Mekkhan spends all his time in a coffee shop in Mechanicsburg, and certainly does enjoy his coffee. During the first attack on Mechanicsburg, there's a caffeine dispensing assistant at his side. He has even written a textbook on coffee preparation (under a pseudonym): Bean There, Done That.
Basically the Fatal Flaw of every Spark in the world. Entering "The Madness Place" grants them incredibly powerful focus, but it makes them entirely oblivious to the potentially disastrous results of their creations.
Specifically, Aaronev Sturmvoraus and his dying daughter, though certainly said by others in this world.
Myth Arc: One of the best webcomic examples. The foreshadowing starts with the fourth strip of the first chapter, with hints about the phenomenon scattered over many, many volumes — and a full explanation has still not been given.
Also basically all of the Heterodynes (prior to Bill and Barry) have these.
If these things are any indication, all strong Spark families tend to be this way.
The Queen of England is only mentioned in hushed tones, even though the only British member of the cast is Wooster. It's implied that she is immortal and that she exercises mind control over the entirety of the English Isles.
"* Oooh, what naughty little devices, to turn upon your creator! Oh! Indeed, my foot is in such excruciating pain! I shall construct a device that will give you such a whack, see if I don't!"
Necessarily Evil: Any Spark who wants to be a good guy sometimes has to turn into a raging madboy just to keep the million separate interests from coming apart. Klaus, Gilgamesh, and Agatha have all found this out. Tarvek, who considers himself an Anti-Villain, even took part in an unwitting demonstration:
Tarvek: (smashing two feuding Dingbots together furiously) I am not enjoying this — but I can keep it up all day if necessary! Gil: Hee hee!... That's a really good impression of my father!
A plot point has significant individuals from the past killed by a machine made from "farm machinery and pork products", which turns them into a string of sausages. Hard to confirm that.
Not to mention, Othar Tryggvassen, GENTLEMAN ADVENTURER; he's been tossed out of two airships on-screen, within the same chapter. Gil doesn't even consider the possibility that he died, having seen him come back from the same or worse so many times.
Gil is also Genre Savvy enough to find it suspicious his father's body is never found. Between what the readers were told before and Boris's comments that the Baron ordered his son to be immediately named head of the empire should he be suspected dead, it's indeed almost certain his death is a ruse.
Before she was even aware of who she really was, Agatha lashed out at a minion grabbing her butt. Turns out her Command Voice inherited from her mother prompted that minion (who was a revenant of the Other) to activate the Slaver Engine that was brought onto Castle Wulfenbach for study.
Zeetha's presence during the standoff at the circus camp at the end of the Sturmhalten arc distracts Klaus long enough for Lucrezia to wasp him.
Agatha activates her own "Lion" device to prevent the Castle A.I. from stopping her from intentionally dying. This permanently destroys the A.I. and lots of other systems. All over the city. Subverted because she found a part of the Castle A.I.. After hooking the A.I. back into the castle, it thanks her for the EMP blast since it destroyed the rogue programs, making it easier to control those parts of the castle. She still has to fix everything, though.
Lampshaded by Violetta on this page when she discovers that Gil and Tarvek have somehow missed the poison that was on the hairpin that Zola jabbed Agatha with.
Dr Sun takes down the Baron's escape clank — by himself — and enforces Klaus's bed rest in order to stop him killing himself from the strain. Awesome — until we learn that, in keeping Klaus in the hospital, Sun's unwittingly exposed him to Anevka!Lucrezia, which is more or less what Klaus feared. Oops.
"And that was the last time Professor Phosphorous visited the fireworks factory. Or anything else, really."
"The Nuremberg Pudding Incident", rumored to have involved the Professora herself. One of the official scents is based on it.
The Opera Synopsis again, where practically every event mentioned is a Noodle Incident. The logistics of someone being trapped in a bonsai hedge maze will likely forever be a mystery to us. In a Reddit AMA with the Foglios, a reader asked if the bonsai hedge was an artistic license take on the thorn barrier erected by the Castle after Klaus froze time in Mechanicsburg. The response: "It is now." It must have taken such actions before.
About half the things Gil, Tarvek, and Zola did inParis.
The entire concept of the Island of the Monkey Girls was one for a long time. It was eventually confirmed to be a night club in Paris... but when a fan asked what Zola thought Gil could have done to get himself imprisoned in the Castle, where the Empire sends people it wants to disappear, the only explanation supplied was "Zola was Head Waitress at the Island of the Monkey Girls Theatre and Showbar in Paris." So that's still an enigma.
No One Could Survive That: Othar. Being thrown out of an airship and surviving is among the least of his feats. From the radio play:
Not Helping Your Case: Tarvek denies having any part in the plan to usurp the Wulfenbachs by installing a fake Heterodyne — his plan was orders of magnitude better!
Nothing but Skulls: The floor of the chapel in Castle Heterodyne is covered by the skulls of those who claimed to be a new Heterodyne master — and failed. The Castle even left a nice empty spot for Agatha's skull...
Nothing Is the Same Anymore: After the Time Skip, everything has changed. Mechanisburg is sealed, along with the Baron, Gilgamesh now leads the crumbling Wulfenbach Empire, and Agatha is on the run from everyone.
Agatha began the comic with an item that forced her to Obfuscate Stupidity. It's a locket given to her by her Uncle Barry to suppress her Spark, so that The Heterodyne Boys' numerous enemies wouldn't try to kill/manipulate/etc. her.
Gil appears to have spent most of his life doing this. As a child he hid his Spark, and in Paris he pretended to be a much worse student than he really was. It was only after returning from school that he was finally able to stop doing it and fully be himself.
Although we haven't seen the details yet, the apparent Badass Bystander Higgs has been spotted chatting with Castle Heterodyne about Heterodynes from centuries ago, and it sure sounds like first-hand accounts.
Wooster apparently tried this, or at least Obfuscating Normal, on Gil, to infiltrate Castle Wulfenbach. Gil was onto him, but played along until he could make more use of Wooster as a British secret agent.
After Martellusis first shown to have replaced his left hand with a mechanical prosthetic, the next page, when originally posted, depicted him opening a bottle with both hands clearly visible, both flesh and blood. This was fixed when it was brought to the Foglios' attention.
At another point they also had to go back and correct a strip which showed post-poisoning Dimo with two arms.
Maxim as he realizes that, since he has Old Man Death's hat, every Jäger around is going to fight him for it.
Mamma Gkika when she sees that the previously unstoppable falling object heading toward the cathedral contains Baron Wulfenbach himself — or the fact that he seems to be carrying a bomb. Probably both. Most of those who saw the contraption for the first time have a small Oh Crap moment when they realize that the castle's defenses weren't stopping it.
Brother Ulm has this reaction, when it turns out that his new passanger is Agatha Heterodyne. He almos presses the ejection button.
Agatha:Hey, Gil! All of Paris is about to go up in flames, and Zola has her head caught in a bucket! Up and at 'em, Hero Boy! Gil: Hm? A bucket? Again? Okay, I'm comin'. Agatha: (shooting a sideways glance at Zola) Yeeeess. I suspected as much.
Old Master: Dr. Sun, quite capable of singlehandedly disassembling any number of clanks — and who taught Klaus and Gil quite a lot about martial arts.
"Two minutes and she hasn't killed anyone!" "A new record!"
Omnidisciplinary Scientist: Though Sparks do specialize, it appears that most of the really strong ones can stitch a living being out of spare body parts as easily as they can build a mechanical AI... or design an electric death ray or a giant airship. Only minor Sparks appear to be restricted to a discipline, as opposed to simply being best at one
Gil: Seven broken ribs. Severe fracture, right leg. Fractured clavicle. Some crush injuries, but the kidneys appear unharmed. First and second degree burns on upper back and lower legs, third degree on the lower back. Four broken fingers, three broken toes, sprained and bruised muscles throughout — major and minor lacerations, and a concussion. Klaus: I've had worse.
Von Zinzer. Good news is, he has a lot of experience dealing with Sparks, which also gives him lots of Genre Savvy, though he's also somewhat fatalistic — he's resigned to the fact that having to work for Sparks means he could be blown up, eaten, ripped apart or otherwise brutally killed at any time. No wonder he can be so snarky. Given the large number of Sparks and Spark minions he has recently been hanging around with, he is sometimes literally the only person in the room who is not crazy.
On a much more serious note, later on when Agatha is trying to power up the Castle, Gilgamesh's behaviour is extremely off, and even Franz notices it despite having never met him. Turns out that he's been brainwashed by Klaus.
When it is revealed that Klaus's mucking about with the space-time continuum has attracted the attention of an Eldritch Abomination, Castle Heterodyne freaks out.The Castle is worried.
Orifice Invasion: The means that Slaver Wasps enter the body and enthrall someone is through the mouth.
Our Hero Is Dead: And buried, complete with digging up the body and cloning a replica to make sure it's really her. The corpse was doctored to make it look like Agatha, but the cloning gave the deception away, as the cloned body was not hers.
Our Founder: In "Jägermonsters to the Rescue", it turns out that in Agatha's two-year absence, Gil has topped Mechanicsburg's city walls with towering statues of Agatha. Dimo describes them as being over 150 meters tall. For the non-metrically inclined, that's 500 feet. The ones at the entrance of the valley are said to be even taller. Agatha is... less than pleased.
Agatha: I... I am going to kill him.
Our Dragons Are Different: We've seen three dragons so far: Franz, the Great Dragon of Mechanicsburg, some pompous red dragon that was part of the Wulfenbach forces attacking the city (Franz now has his hat), and a Great Sky Wurm that Gil won as spoils when the Polar Lords attacked him during the Time Skip that he traveled the long way through.
Our Vampires Are Different: Dame Aedith is a vampire hunter, despite the fact that no vampires have been seen. Although there was this little gem...
Wooster: Um... we're not going to meet some ancient undead Heterodyne vampire or something, are we? Carson: Oh, and wouldn't that be the perfect capper to my day. Wooster: Um, actually, that wasn't a "Ho ho, don't be silly old chap." Carson: I ain't being paid to lie to you, Brit.
Our Zombies Are Different: Several different types. Besides "traditional" zombies of the Type F or Type V variety, they also have Jaegermonsters and Constructs, which are essentially Type A creations, and Revenants, which despite the name are more a cross of Type T and Type P, Parasite than Type R zombies: infected by a slaver wasp, they are like sleeper agents, going about their business and not even realizing they are infected until triggered to fight on the behalf of "the Other".
Out-Gambitted: The Knights Of Jove swept in to rescue Agatha for their own nefarious purposes, at which point Klaus revealed virtually his entire army had been waiting in hiding for them to show up. And they weren't even the real reason he did it.
Most notably, Gil dropped out of the story early in Volume 4, reappeared briefly at the end of Volume 5, and finally reentered the story for real in Volume 7.
Lots of other characters from the first arc disappeared after it was over and have either not returned or only showed up again in the third arc. The end of the second arc also sent a large number of supporting characters offstage. It also happens within arcs: Klaus has done this more than once. Given the webcomic format, the size of the cast, and the demands of the story, it's inevitable that it will keep happening.