Filler Strip: Radio Theatre Breaks, Short Stories, Fairy Tale Theatre: Cinderella, and to a lesser extent, Heterodyne Boys Stories and "The Storm King Opera" synopsis, as the latter two contribute to the overall mythology.
In-universe example; the character of Big Guy Punch in stories and stage-shows is reduced to comic buffoon and Butt Monkey. Among the secrets kept from Agatha her whole life was that the quiet, competent blacksmith she knew as her father was Punch. The Jägermonsters who knew Punch try to give an actor advice on how to play him authentically, but all of it requires casting out what makes his act so successful.
Klaus' characterizations in many Heterodyne stories has undergone similar treatment, being rewritten as an excitable cowardly braggart. Although he's now the unquestioned conqueror of the entire continent, Klaus permits this impertinence for one simple reason: he thinks it's hilarious.
Klaus' "Götterdämmerung!"note This isn't a curse word in the usual sense; the second part of the word is closely related to English "dim" and the word/phrase (German is highly agglutinative, so sometimes these are the same thing) really just means "twilight of the gods". It is most commonly used as a synonym for "Ragnarok" (as in, the Apocalypse of Nordic mythology).
Zola will mutter "Merde!"note French for "shit" when riled up enough.
The whole missing tale of the Storm King that Klaus told the Author Character is either Klaus foreshadowing things to come or sending a message to his son in a very cryptic manner, so that Lucrezia wouldn't realize what he was doing.
Agatha being able to order Gil not to die on her foreshadows Klaus' discovery that Gil is a revenant. Although that likely was faked, since the wasp-detector was not reacting to Klaus, and we know he's got one!
It's mentioned several times that the Storm King Conspiracy needs the Heterodyne heir alive for their plans. Guess who Tweedle tries to escape Mechanicsburg with once things go south.
For the Lulz: Apparently, this is why Castle Heterodyne kills people. Because it "will be fun". All Heterodynes before Bill and Barry also seemed to have this as their primary motivation. Klaus even claims in his Storm King story that Clemethious Heterodyne always smiled, even while sleeping - because he constantly thought up new ways to torture, kill etc. people.
Funetik Aksent: "De Jägers hall talk like dis, sveethot!" Even their clappingis accented. The novels explain that it's an ancient Mecanicsburg accent, carefully maintained as a point of pride. That's why a random mother Gil runs afoul of in Mecanicsburg shares the accent.
Funny Background Event: The Foglios love this. In particular, it's worth reading any notices, signs, control labels, advertisements or scripts that appear.
Theo's idea of a good home-brewed liquor can be expected to be at least 200 proof, and have other... interesting ingredients. Note that 200 proof is pure alcohol. Also note that under normal circumstances, opening a container of pure alcohol outside of laboratory conditions will cause it to be diluted by the moisture in the air. Maybe part of Theo's talent as a Spark makes him a Mad Moonshiner who can make impossible drinks?
Generation Xerox: Several of the characters apparently look almost exactly like younger versions of their parents, enough to confuse Lucrezia in the cases of Tarvek and Zola. Gil appears to resemble his father as well, but it doesn't get him recognized as the Baron's son.
Also, this entire exchange between Gil and Tarvek.
Tarvek: So, Wulfenbach — just checking — is this going to be some kind of macho exercise where you insist on battling a potentially superior opponent alone in some kind of misguided attempt to "prove" your intrinsic worth? Gil: No, no! I'm only that stupid in front of Agatha! Tarvek: Drat.
Gentle Giant: Punch, apparently, though most people who didn't know him assume he's just Dumb Muscle. Also possibly a Genius Bruiser, though the evidence for that comes from the Jägers who are... not the best at determining who's "schmott".
Belloptix: But... didn't he have a... lighter side? Maxim: Oh yah! He build very amuzing toys for de orphan cheeldren!
The Girl Who Fits This Slipper: Deconstructed during the Cinderella parody. Tarvek has Cinderella's slippers and wants to find the girl who fits them, but Gil argues that the shoes, size nine-and-a-half, would fit too many other women. Tarvek soon brings out a picture of Cinderella, but Gil says they no longer need the shoe.
The Baron's approach to governance can be summed up thusly: "Don't make me come down there." So getting the Baron involved in a problem is perceived this way.
Master Payne explains his decision to notify the baron about Passholdt being overrun by monsters, over Agatha's protest that they should help instead:
Payne: Could you burn down people — women and children — even if you knew they had become monsters? The Baron can. The Baron has. I respect him for that but I don't want to be him.
The Baron's own personal Godzilla Threshold involves plots having to do with Revenants or The Other. Unfortunately, this means Agatha is number one on his Most Wanted list because of her relation to and possession by Lucrezia. His response to Agatha gaining full control of the Castle and Mechanicsburg is to fly down himself with a "black level device" which turns out to be a city-wide stasis-field generator.
Goggles Do Nothing: Dimo (green Jäger with 5 o'clock shadow, wearing an olive-drab cap with mustard trim and a yellow ostrich plume stuck in).
Good Is Not Dumb: Everyone thinks that just because Gilgamesh Wulfenbach never built a Death Ray and almost never screams at people or beats them up to get them under control, they can push him around and act like he's nothing. Whenhe's finally pushed over the edge, he shows the entire world that yes, he does know how to build a Death Ray, and yes, he's perfectly capable of kicking the crap out of Europa to protect his father and not-girlfriend.
Grand Theft Me: Lucrezia attempts this on several occasions on different characters. How successful she is varies:
Agatha is able to shrug it off, thanks to her locket, later by sheer force of will.
She later succeeds at it fully with Anevka.
Her try with Zola fails, because Zola's brain was prepared with a trap for exactly that occasion. Zola now has a replica of Lucrezia's psyche inside her mind and can sift through the thoughts and memories of it more or less at will. Due to Zola's injuries and her overdose on MoveIt, nobody knows who is in control now.
It would appear that The Baron has done this to Gil as of the summer of 2014. Possibly to get out from under the control of the Other.
Gil once started speaking French while delirious. Translated: "Excuse me sir, but where is the catastrophe?" Gil spent a lot of time in France when he was younger — and he spent so much of that time coming to the rescue of danger-prone ditz Zola that it's just sort of reflex for him to keep an eye out for disasters when she's around.
Jägermonster = hunter-monster, Geisterdamen = ghost ladies, Sturmvoraus = storm ahead, Wulfenbach = "Wolf's stream" (not strictly correct, but German is dialectual and it's a place/family name). Of course, since this story is apparently set in a 19th century Central Europe not totally unlike our own, this is more of a Translation Convention, since German actually would be the lingua franca of the setting.
Though according to the novels, the official language of the Wulfenbach Empire is actually Romanian.
There is one straight-up bit of gratuitous German when a Jäger uses "Jägermonstern" as a pseudo-German plural for his own kind. The German plural is in fact "Jägermonster", which of course sounds rather odd in English.
Holzfäller, the fake surname Gil used in Paris, translates as "lumberjack".
Sturmhalten, the home of the Sturmvoraus familiy (see above), literally means "to keep storm", a.k.a. Storm Keep. This matches with Mechanicsburg, burg being old germanic for "castle". Wulfenbach started as a smaller house, so their fortress is just Castle Wulfenbach.
The Guards Must Be Crazy: When Gilgamesh needs to get back onto Castle Wulfenbach to take control of the Wulfenbach armies around Mechanicsburg, he needs to get past a number of guards who have never dealt directly with him and thus don't know what the Baron's son looks like. Sleipnir tells him to wear the Nice Hat given to him by the Jägers. You know, the giant purple and red hat with "Gilgemesh Wulfenbash, Schmott Guy!" written on the front and the flame on top which flares up periodically. Each guard Gil approaches is initially unimpressed and unconvinced, until he fires up the flame. At that point, they believe he really is "Gilgemesh Wulfenbash" [sic] and let him pass. But eventually he gets to one who reacts differently.
Guard: Oh come on. You expect me to believe you— (Gil's hat goes FOOM!) Guard: Just because of that ridiculous— (Gil punches the guard in the face, knocking him out) Gil: When this is all settled, you get a promotion.
The helmet which allows Castle Heterodyne to possess the Seneschal.
In a "Trelawney Thorpe" short story, the crown of King Arthur, which allows Arthur to possess its wearer.
Hat of Authority: Hats might be the only thing Jaegers take seriously. You simply can't be a Jaeger in good standing without a Nice Hat, which makes the over-the-top monstrosity they present to Gil a gesture of magnanimity. Old Man Death also deserves mention.
Haunted Technology: Castle Heterodyne is generally seen as this, and it suits Wulfenbach to let people believe it. The application of Clarke's Third Law effectively makes it so; even characters familiar with the machinery refer to the rooms as "alive".
Head-Tiltingly Kinky: When Agatha is working in the traveling Heterodyne Circus as the psychic Madame Olga.
Baron Wulfenbach says early on that he would rather his men criticize him rather than fear him too much to tell him important information — in fact, the first time we see him, he's testing Gil to see if he'll tell him he's wrong. It's one of the many signs that he's not your average Evil Overlord.
Gil and Agatha seem to prefer advisors like this as well.
Krosp complains that his role as a spy chief leading a group of unaugmented cats was bound to fail because normal cats are too easily distracted to follow orders for any length of time. Years later, when Krosp himself has the opportunity to gather information, he gets hungry...
I Am Who?: Agatha is quite shocked when her parentage is revealed.
Idiosyncratic Episode Naming: Each volume of the print collection is titled "Agatha Heterodyne and the Noun Phrase", where the noun phrase in question refers to some person, place, or thing that does indeed appear in that volume, but is never actually referred to by that name.
Idiot Hair: It's obviously not reflective of her intelligence per se, but Agatha's got a bit of hair that won't stay down; as highlighted in thistwo-partFiller.
Castle Heterodyne declines to reveal information about Airman Higgs to Zeetha, as doing so would require Zeetha to be killed. Not that the Castle objects to killing anyone, but Zeetha is essential to Agatha in the Castle's opinion, so she must be spared.
Carson von Mekhan: Sure, the Heterodynes were dangerous lunatics— but they became our dangerous lunatics!
Moloch von Zinzer stands out because, like the natives of Mechanicsburg, he's a natural minion, but unlike the Mechanicsburgers, he has a certain amount of insight into Spark psychology, and can use this to get them back on target when they inevitably get sidetracked.
The Jägermonsters. It still hasn't been established what it would take to kill one of them, and they are amongst clanks as shock troops — Baron Klaus shows particular respect toward them. When Maxim, Dimo and Oggie are introduced, they'd been hanging in nooses for days, casually observing and commenting on the town. It's implied that Othar conned them into getting into the nooses voluntarily.
Most shocking example is when Gil shot Franz with a sedative through the palm... and he's down for the count in mere seconds, despite being a freaking dragon. On the other hand, Franz only stays knocked out a minute or two.
General Zog: Sir — dere iz a time to twit nancy-boy feetsmen und a time to crush bogs.
In the Blood: Sparkiness is usually hereditary. Spark styles of invention too.
Agatha: I believe another forty-five point three seconds, and I would have exploded or something. Castle Heterodyne: ... or something. Under the circir/circumstances I/I am forced to admit that yo/you are most most likely oneoneone of the family... Agatha: Oh, yeah... I have got to try thatagain! Castle Heterodyne: yesss... most likely, in/in/indeed.