Adaptational Jerkass: The Doctor Strange in this fic appears to be less noble when compared to his comic counterpart. Given the malevolent cosmic threats like Thanos lurking about a guy like Strange has to get his hands dirty once in awhile to assure the universe remains safe. So this is a strong case of Tropes Are Not Bad.
Odin and Thor... sort of (there's a reason the entry is on this page).
Odin was willing to put innocent Russian civilians lives at stake, just for the sake of taking down the Red Room, though it could be argued that the Red Room controlled Russia and there was no real way of getting a stranglehold on them without getting one on the rest of Russia as well - a stranglehold that lapsed the moment the Red Room were squashed. Which seems in character for an experienced and occasionally ruthless commander who's both achieving an aim and making a point.
Thor seems to lack the humility he'd develop from the Marvel films and is more brash and hotheaded when compared to his canon counterpart - though this might be explained by his son's habit of getting into trouble/dying and coming back/being horribly traumatised, which would strain the patience of a saint. And while he went out of his way to have a little 'chat' with Snape over how he treated Harry (on which subject he did have a legitimate bone to pick), he did it in private and thanked him for saving Harry's life. He also later called off Huginn and Muninn when they decided to have a similar conversation in public. And when Snape ensured that Remus lost his job, even then, he restricted his revenge to a small thunder-cloud following Snape around at all times which, while perhaps amusingly petty, isn't exactly a grave offence.
And in the same vein, is Peter Wisdom a.k.a. Regulus Black much the same in terms of being dedicated to protecting humanity from the monsters in the dark, or is he a half-crazed power hungry Manipulative Bastard and an obsessive Hunter of His Own Kind dedicated to forcibly taking control of the Wizarding World and bringing it to heel? Judging by chapter 72, a little from column A, a little from column B. He sees bringing the Wizarding World to heel as the primary means by which he can protect ordinary humanity.
Is Sean Cassidy really a fairly happy go lucky fellow, determined to be cheerful despite it all, and a good mentor, or is that simply amask for a cold, Revenge obsessed master spy and assassin?
Is Harry a remarkably well-adjusted, mature, if snarky kid (considering the Avengers, the latter is inevitable), with the potential to be his generation's Captain America? Or is he a Shell-Shocked Veteran whose snark is a defence mechanism, a de factoChild Soldier with a Hair-Trigger Temper used to using intimidation to get his way, who is slowly developing into a Dark Messiah on par with or beyond Magneto himself? The answer, as Doctor Strange remarks in chapter 75, is that he could quite easily become either depending on the choices he makes. One way he could become a great hero, the other way he could become 'the thing men fear'.
Is Doctor Strange a benevolent Deadpan Snarker and Big Good for the universe who works tirelessly to ensure that the good guys get through largely unscathed and deeply regrets the sacrifices he must make, or is he a spectacularly ruthless Manipulative Bastard running a Xanatos Gambit of unimaginable scale, whose benevolentfaçade falls away when it is not needed, trades on his cultivated reputation for never lying to ensure that people do what he needs them to, turns children and adults alike into his weapons in ways so subtle that they don't even notice and is entirely willing to sacrifice thousands of good people through action or inaction in order to sharpen his tools for a future battle and bring about his vision of a better future?
Chapter 80 reveals the answer: Both. While, yes, he could have just saved the day by revealing everything he knew, it would have resulted in potentially worse results, and none of the friendships and good ties made due to the fight against HYDRA would have happened. He regrets that so many people died, and wishes he could have done otherwise, but had he prevented the deaths of today he would have been unable to stop the disasters of the future.
Crosses the Line Twice: In Chapter 17, Thor proclaims (on Harry spending an instructive half an hour with Tony and Darcy) that Lily will probably return from beyond the grave to strangle him for this. Cue Loki conjuring an illusion of an infuriated Lily. Thankfully, Thor takes it pretty well.
Crossover Ship: It's revealed that McGonagall was the fiancee of Bucky Barnes. It becomes more meaningful when it's revealed that she was pregnant when he "died," and reveals that Hawkeye is her grandson. Meaning that Clint is the grandson of one of the most powerful witches alive and the Winter Soldier, the world's most notorious assassin.
We've also seen the early stages of Lex Luthor/Susan Storm.
Previously, there's been Wanda Maximoff/John Constantine.
Which has since evolved into Harry Dresden/Wanda Maximoff.
There is persistent Ship Tease of Carol Danvers/Harry Potter, with Word of God being rather enigmatic when asked about it - though the general consensus is that it is less a matter of 'if' than 'when'.
Later chapters of Ghosts of the Past are pairing up Diana and Ginny.
Darker and Edgier: Ghosts of The Past is shaping up to be this as compared to Child of the Storm - the villains are much more personal when it comes to going after Harry, something shown in their tactics, while Wisdom tightens his grip on Magical Britain and Harry demonstrates an increased willingness to use the darker side of his psychic powers when pushed.
Designated Hero: Even though it wasn't without reason, Asgard causing the Red Room to collapse by strangling its resources, affecting the lives of the innocent civilians in the process, wasn't a heroic move on their part. In fact, Asgard and the Avengers are more than capable of abusing their power in this 'verse.
In chapter 37, Tony notes that Loki 'has thirty six fansites, seven of which are solely dedicated to working out what he'd look like in tight leather pants'.
Ensemble Darkhorse: Has quite a lot of these thanks to the author's penchant for reimagining characters, as well as throwing in those characters at the last minute, later developing them into prominent figures in the story. The two main examples come in the form of Carol Danvers and Diana of Themyscira, both of which were added in at the last minute, apparently entirely on a whim and praised as original takes on the character. They've both grown from fairly minor characters into two of Harry's closest friends, two of the more badass characters in the story and bona fide fan favourites - in a poll of favourite new or reimagined characters, Diana was the runaway winner, with Carol being joint third behind (unsurprisingly) the Winter Soldier, who's even more of a Woobie than usual thanks to the sections from his perspective, and sharing third place with Huginn and Muninn. Indeed, Carol's grown into a full on Breakout Character, being close to a Deuteragonist with Harry, and she and Harry are now the Fan-Preferred Couple (with Harry/Diana being close behind).
Then you have Lucius Malfoy who is the epitome of From Nobody to Nightmare. He started out as just an underling for Lord Voldemort but gradually grew into not just a magnificent bastard but into a more formidable opponent for The Avengers. He even succeeds in taking over the world, even if it was temporarly. While doing it with such style and sophistication.
Jean-Paul Beaubier/Northstar and Uhtred Ullrson. The former is a fairly minor member of the X-Men and the latter began as a minor OC Asgardian who was apparently set up to be The Rival to Harry. Both become two of his closest friends, with the former developing into a deceptively harmlessCamp Gay flirt with considerable Hidden Depths, the ability to pull off an absolute absent minded Sherlock Scan and be arguably the mostruthless of the kids in a fight, as well as being the Only Sane Man. Also, as of chapter 60 he seems to be this world's version of the Flash. Uhtred, meanwhile, is developed from a fairly Flat Character whose primary motivation was resentment at the attention Harry got simply for existing, while his hard work barely got him any, to (one shared Near-Death Experience later) Harry's loyal (if snarky) oathman and Sworn Sword, a major league badass who knows his way around an axe. Also, he and Jean-Paul are pretty much a de facto Battle Couple.
Sean Cassidy is added for the sake of variety to Peter Wisdom's Excalibur squad, but despite initial uncertainty by fans, grows into a popular mentor figure to Harry, something helped by his nature as an Adaptational BadassGrandpa, something helped by the way he gently reins Harry in when he looks to be going too far and the bond he has with Luna Lovegood.
Fan-Preferred Couple: while neither of these pairings has come about, fans have vocally called for Harry Potter/Carol Danvers, on the grounds of the considerablechemistry the two share despite their mutual insistence that they are Just Friends, over the Word of God stated original plan of Harry/Ginny. While the author has been enigmatic about the former, the latter has been confirmed to have been removed, as part of a raft of grand scale changes to the future of the story.
The story also manifests an example of this trope, with a strong Bucky/Natasha dynamic woven in, despite the fact that the fic as a whole is heavily based on the Marvel Cinematic Universe, with not even a tiny bit of Bruce/Natasha chemistry (despite it being MCU canon).
Relatively early on, the author created a poll out of curiosity to see who fans would prefer Harry to be with. Jean Grey won by a clear margin, with Emma Frost and Hermione Granger not far behind, tied in second place. Based on Word of God, Harry's not going to be paired with any of them - Jean Grey is his cousin and Cool Big Sis, though a letter written by a version of Harry from the future notes that she's 'disconcertingly attractive' and pretty definitely shipped with Scott Summers, Emma Frost and Harry are stated not to get on at all and the narration has on more than one occasion noted that Harry very rarely notices that Hermione is female and is 'about as attracted to her as he is to mould'.
A more recent poll shows that Harry/Carol is now by far the most popular potential ship amongst the fanbase, with Harry/Diana being a relatively close second.
"Funny Aneurysm" Moment: Harry's snarky remark that he's very attached to his arm and likes to think of it as being very attached to him gains a darker undertone when it gets blasted off by Magneto during their fight as the Red Son.
Carol's crack about Harry's temper being like "Carrie as directed by Michael Bay" at the start of the Forever Red arc takes on a dark twist at the end when Harry snaps just like the titular Carrie and becomes the Dark Phoenix.
Knowing Nimbus, it's plausible that this was intentional.
If you had any doubts about the identity of 'The Hidden World', as the author note mentions, translating 'The Hidden One' into Ancient Greek reveals the name of the planet. Krypton.
The title of Chapter 34 ("Fool's Gambit") is both a reference to the insanity of Harry's Crazy Enough to Work plan and the name of a chess strategy which relies on acting fast, Refuge in Audacity and taking the opponent offguard. Much like Harry's plan.
Growing the Beard: The fic really hit its stride right around when The Winter Soldier is introduced and starts wreaking havoc.
Seeing any scene involving him and Pepper may be awkward since Civil War implied that they had an off-screen break up.
Strange's Badass Boast to Jean in chapter 75 of Child of the Storm, "Miss Grey, I am the Sorcerer Supreme. Mistakes and misapprehensions are for other people." It takes on a darker hue in light of the fact that, as of chapter 9 of Ghosts of the Past, he appears to have made a mistake — and an absolute whopper too. Not only that, but one which directly affected her as well. Of course, it could also be taken as a statement of intent, that he believes that they should be things for other people, and he's trying to rectify them.
During the first book's Final Battle, Thor casually shows that he can still throw around lightning even without his hammer. Then along comes Thor: Ragnarok, and he has to go through a whole movie and an epiphany before he can figure out how to do that.
The first book's final battle also features Hulk smashing Chthon the same way he did to Loki, with the latter commenting on how gratifying it is to see it happen to someone else. Then Ragnarok comes along, and Hulk does that to Thor, with Loki being ecstatic about it.
In Child of the Storm chapter 75, Strange tells Carol that her willpower is without equal, and she snarks that unless being really stubborn is going to make her bulletproof, she doesn't see how that'll help much. Guess which magical device he gives her? The Green Lantern ring, which works on willpower and can, in fact, deflect bullets (or do a lot of other stuff).
Seeing how Steve hooks up with Sharon Carter in the Marvel Cinematic Universe can be a bit awkward when you realize that she's his great-granddaughter in this fanfic.
Invincible Hero: The Avengers and Asgard, as of Ghosts Of The Past. Especially given the way they mowed through the Red Room with minimal effort once they pinned them down.
Averted with Harry himself. The author himself has repeatedly and emphatically stated that, despite his newfound powers, he's still struggling to figure them out, and will be on the wrong end of more than one beating.
Jerkass Woobie: The Disir. They may be villains, but you can solidly blame Bor and Malekith for what happened to them.
Chapter 16 is literally called "Magnificent Bastards," which is unsurprising considering it focuses on Lucius Malfoy and Loki.
Doctor Strange is basically Havelock Vetinari with magic powers and an insight into the future, perpetually being several steps ahead of everyone else and, more to the point, using them as pawns - something which proves to be Paranoia Fuel for Lucius in chapter 72 of CoS. Chapter 75 gives an insight into the sheer scale of his operations. It turns out that even when he gets hit by a Spanner in the Works such as Essex being hidden from his Sight, he's still capable of some pretty decent Xanatos Speed Chess. Even the Dark Phoenix mess ends up being turned (somewhat) to his advantage.
Moral Event Horizon: Gravemoss goes shooting over it in chapter 21, enjoying himself immensely as he does.
One-Scene Wonder: Not strictly confined to one scene, but where the Winter Soldier is concerned, this applies.
While not yet a recurring role in Ghosts of the Past, Voldemort's presence has left a profound impact among the Avengers & Harry himself.
The same couple have also generated "Magic Lantern."
Ron the Death Eater: Refreshingly not with the character himself, who actually comes off as the Only Sane Man when compared to the rest of the deeply eccentric cast.
Snape, however, is not so lucky. While not being outright despicable or villainous, and having his good deeds (namely, protecting Harry) acknowledged, the fic does make him come off as a petty individual who uses his past grudge against James to torment Harry. Sometimes the treatment goes into Butt-Monkey territory.
Dudley. Oh dear Lord, Dudley. Far removed from the book character who, while a bullying brat, was complex enough to be one of the few members of the Dursley's to develop into a better person and accept Harry. In this version, he's just an absolutely vile monster who later becomes Sinister's Stupid Evil dumb muscle.Word of God explains that Dudley as he is now is basically the result of several years of having every single one of his darkest whims and desires catered for and encouraged by the Red Room. It also doesn't help that while Dudley did take several levels in kindness after the events of the fifth and sixth books in canon, partly thanks to the perspective forced on him by the Dementor attack in the fifth book, this is a Dudley for whom none of that happened.
Slow-Paced Beginning: One criticism is that the story starts slowly and takes a few chapters to find its stride.
Spotlight-Stealing Squad: Averted. The author himself worried that he was reaching this point in Child of the Storm by putting a lot of focus on Loki, which was why he balanced it out to give the other characters a chance to shine.
The Woobie: The author managed to take Harry's canon Woobie status and crank it Up to 11. As of the aftermath of the Forever Red Arc, it's now much, much, MUCH higher than eleven. So much so that it makes what he went through in canon look relatively tame in comparison.
Unexpected Character: The general consensus is that no one was expecting Dudley to return as the Blob.