Anna Fang, badass airship pilot and swordswoman extraordinaire. Like Shrike, she was not only resurrected as a Stalker but eventually became the Big Bad.
Although General Naga appeared briefly in Infernal Devices, he became a major character in A Darkling Plain, thanks to being a badass and likable general and his epic Heroic Sacrifice.
Harsher in Hindsight: The Show Within a Show features Hester being made conventionally attractive, a process which included reducing her scarring to a small cut. The film adaptation would end up doing exactly this, with the director and Peter Jackson saying that the character not being pretty made Tom being in love with her unrealistic, even though that's what happened in the book. Even worse, Word of God says Hester was made heavily scarred precisely so Tom would come to love her in spite of it, finding it more interesting than two glamorous people falling in love.
That being said, arguably this Adaptational Attractiveness is justified by the limits of the medium- after all, unlike in a book, such extensive prosthetic effects take time and money to pull off on-screen. Not to mention, even if they could successfully translate Book! Hester's disfigurements to live-action, there is always the risk of alienating the audience either because they looktoogood or don't look goodenough.
Heartwarming Moments: In A Darkling Plain, the scenes where Fishcake and Anna find Sathya's hermitage in the mountains, and start acting like a family... Especially the scene where Anna carves a toy horse for Fishcake, and he acts like it's the most beautiful thing he's ever seen. Sniff.
Les Yay: Plenty between Sathya and Anna Fang. Sathya created the Green Storm and revives Anna Fang because of this. Even the Stalkerized Anna goes back to Sathya. Confirmed by General Naga in the last book.
Mst3k Mantra: The idea of a mobile city-eating cities is absolutely ridiculous and raises so many logical questions that are realistically unanswerable (and this isn't even getting into the idea of floating cities, tiny airships, and other more fantastical elements), but it is the basic premise of the series, so you have to accept it.
Throughout Mortal Engines, Katherine Valentine discovers that the city she calls her home is not as shiny as she thought, that most inhabitants don't consider her as one of them anyway, and that the person she trusted the most is a liar, a thief and a murderer. Add the death of anyone else whom she ever cared for and by the end of the book, she's become a Determinator to the point it's heartwrenching.
Tom and Hester also count as one too.
Valentine might be a Jerkass Woobie; he did terrible things, but he wanted to make a better world for Katherine, and this backfired spectacularly.
Cliché Storm: The movie was strongly criticized for its bland story, which took many, many common plot elements from other sci-fi, post-apocalyptic, or fantasy works, in particular Star Wars, without really doing anything new or unique with them.
Complete Monster: Thaddeus Valentine is the head of the Guild of Historians and the second-in-command to the mayor of London, Magnus Crome. Introduced observing the mobile city of London devouring a small mining town, it was revealed that prior to the main story, Thaddeus personally murdered the mother of the assassin—and his own daughter—Hester Shaw, and scarred Hester's face in order to gain an Old Technology for his own agenda. When one of the other Historians, Tom Nasworthy, found this out, Thaddeus released the dangerous criminal Shrike and sent him after Hester and Tom. It was revealed that he uses said Old Technology in order to activate a weapon known as MEDUSA that could destroy the Shield Wall that protected the static settlement known as Shan Guo so that he could make it his new hunting ground. When the mayor found out about Thaddeus's plans, Thaddeus murdered him in cold blood. When his plans of destroying the Shield Wall failed, he then orders his henchmen to execute London's control crew and plans to ram London into the wall. His own daughter Katherine called him out on how his only goal was to gain more power.
In the museum archives, during the chase of Seltzberg, Pomeroy shows concern over the "American deities" getting tipped over. The camera pans over to rusted over statues of two Minions.
While showing Kate around the museum, Tom briefly explains to her the Screen Age, AKA, our current modern age. Tom mentions to her that their tech was considered advanced enough that they might've forgotten how to read and write... while the camera pans to some iPhones in the display.
Director Displacement: The name of producer and co-writer Peter Jackson showed up more in advertising and discussions than that of the actual director, Christian Rivers.