The Adjectival Heroine: She's the "Great and Powerful" Trixie, thank you very much! What's more, she improvises new heroic epithets to match her mood and the virtues she claims to be currently exemplifying.
Advanced Ancient Ponies: Four thousand years ago Manehattan was the city of the "titan towers" — immense skyscrapers, beyond the technology of present-day Equestria to duplicate. The towers fell in the Cataclysm that ended the Age of Wonders. The Manehattan Coven wants to bring about another Cataclysm and destroy the modern city.
A Goddess I Am Not: Princess Celestia. These are her thoughts as she lashes herself with scorn for her her series of errors that has led up to Equestria facing the threat of annihilation by Nightmare Moon:
They worship me as a goddess, no matter what I tell them — do they not know how deeply flawed, how utterly fallible I really am?
Alien Invasion: The Shadow Wars. The Shadows, beings of "anti-life" from another Universe, are invading the Earth and the Return of Nightmare Moon is only one part of the first invasion. In its early stages this is mostly a matter of infiltration and Demonic Possession, but later stories in the verse make it obvious that this will eventually escalate to an outright Lensman Arms Race.
All Part of the Show: The reason why the crowd does not panic and run when a battle between thirteen Shadow Ponies and an Alicorn erupts right in front of them.
Apocalypse Maiden: Princess Celestia fears that her sister Luna, as Nightmare Moon, may have this destiny.
Arc Words: "The show must go on." The reason why Trixie is willing to keep on playing to the point of exhaustion and, ultimately, why Illusion is willing to fight the Shadow coven.
Asexual: Trixie seems to be this, as she very much did not enjoy her single sexual experience (mentioned in flashback), to the point where it led her to avoid someone she considered a friend.
Believing Her Own Lies: Trixie's main obstacle to personal growth is that she has convinced herself that she desires neither love nor friendship, and thus isolates herself — when it's fairly obvious that she simply doesn't know how to get along with other ponies.
Big Applesauce: Not only is Manehattan the Equestrian equivalent of New York City as in canon, but "Tompkins Town" is based on a particular Manhattan neighborhood. It should be noted that the author was born in New York City and lived there most of his life.
... she never flaked on a show, never missed her time, never short-changed an audience. That was her code of honor, her integrity as a professional show-mare. "The show must go on," that was a good summary of her life and her credo.
The Conscience: White-Beard the Grey, for Trixie. She's well aware of this, too.
... sometimes ... when she was tempted to do something really bad, his image came before her, and she knew that she did not want even his theoretical disapproval. She supposed he had become the symbol of her conscience, though she wasn't sure that such a wonderful mare as herself actually needed one. Still, the thought oddly comforted her. It was almost like having him back for real.
Cute Monster: Granny Pie's Least Noticeable Grand-Daughter, named (in one sequel) Claire Quartz Pie. She's a huge Eldritch Abomination who is basically a ponified version of Wilbur Whateley's Twin. She's also an innocent, nice and generally sweet creature who loves Ponies and life in general. Her most powerful attack is weaponized love, and it is only lethal to the NightShadows. Her main goal is to open the way for her father Paradise, a creature whose declared purpose is to spread happiness and joy. Her main desire (as revealed in the sequel is to find love and friendhip. You just want to hug her, and it would probably feel nice because she's warm and very fluffy.
Cute Witch: Trixie herself. Possibly approaching Hot Witch territory, depending on who one asks.
Dark Is Evil: The Night Stallion, his Shadow Coven, and the Shadows in general.
Dark Is Not Evil: Luna, who in the background overcomes the Shadow and is purged of her evil. She's still dark-themed as Luna, just no longer evil.
Does This Remind You of Anything?: The Shadow Coven are essentially (occult) terrorists serving (alien) foreign masters who plan to "tear down the towers" of the city of Manehattan, a Fantasy Counterpart City to New York. Later, Celestia realizes that this and similar attacks elsewhere are just the first battle of the Shadow Wars. Didn't something similar happen, and isn't it happening, in our world?
Double Meaning: Everyone assumes that Trixie used "The Alicorn Illusion" (an illusion of an alicorn) to frighten away hecklers. Actually, it was "The Alicorn, Illusion" the Manifestation of an actual Alicorn, whose name is Illusion.
Dream Sue: Trixie is very much a Mary Sue in her own mind — beautiful, powerful and always not merely the heroine but the insufferably perfect heroine of her own story. This is why she constantly invents and applies new heroic epithets to herself. To some extent she seriously believes this, to some extent it is obviously a game she is playing in her mind to endure the vicissitudes of life.
Exact Words: Trixie decides to have her contract rewritten to specify her time on stage as "until dawn" instead of specific hours, purely for aesthetic purposes. This comes back to bite her on the flank when dawn fails to happen for several additional hours, and she has to extend her performance accordingly.
Fear Aura: One of the main powers of the Shadow Coven is their ability to induce fear. We get to see how a victim perceives this power when the Night Stallion uses it on Trixie.
Friendless Background: Trixie's alienated from her family, and mentions having had two friends in her internal dialogue. Her Mentor White-Beard is dead; she fled Piercing Gaze when they wound up making love one night, and so she walks alone.
Gravity Mistress: Princess Luna. Her most powerful attacks are force beams and the projection of beam and point gravitic singularities.
Good Ponies Have Good Sex: Subverted by Trixie and Piercing Gaze. Trixie has a very low sex drive and severe trust issues; when she and Piercing have sex for their first and only time (first and only time ever for Trixie) it disgusts her so deeply that she flees the city of Baltimare. She regrets this action because this means she also lost a good friend. (Her Pride prevents her from trying to make up with him). Despite this disaster, it is very obvious from Trixie's thoughts that she still cares about him, and the sequel A Long Night At The Hippodrome makes it obvious that Piercing still cares about her, too.
Hair-Trigger Temper: One of Trixie's emotional flaws. Makes her even more of a misfit because her species is less aggressive than the human norm. Her Superpowered Alter Ego, the Alicorn Illusion, seems to be nicer.
Heroic Spirit: With a little help from what may be the ghost of White-Beard the Grey, Trixie overcomes the fear aura of the Night Stallion and — despite being well aware that she is facing a band of ruthless black magicians — refuses to let them shut her show down. You rock, Trixie.
I Work Alone: Trixie's explanation for why she's a one-mare show. The truth is that she's too abrasive and unreasonable to make or keep friends. Piercing Gaze tried to get her to join a bigger troupe, but then she ran away from him.
Inferiority Superiority Complex: Trixie, big time. She's a lonely little unicorn who constantly convinces herself that the problem is that she's just so great that no one else understands her. It's notable that she tones this down when thinking about ponies whom she feels actually believed in her talent, such as White-Beard and Piercing Gaze.
Insufferable Genius: Trixie is arrogant and obnoxious. Trixie is also a really skilled stage magician, who is capable of improvising and successfully performing without rehearsal new tricks when under considerable pressure, as she demonstrates in this story.
Intelligence Equals Isolation: One of Trixie's main theories as to why she is friendless. Interesting, given that this was also one of Twilight Sparkle's defining attributes until she moved to Ponyville.
It's All My Fault: Princess Celestia blames herself for failing to prepare Equestria sufficiently to deal with Nightmare Moon's coming.
Celestia (thinking): Why, after a thousand years of preparation, had it come to such a desperate pass? I knew this was coming, I arranged its coming, I should have been more ready for it! Not for the first time, she briefly reviewed her mistakes — talents encouraged too much or too little, students whom she had failed and who had thus predictably betrayed her.
Jerk with a Heart of Gold: Trixie, who is arrogant, bad-tempered, obnoxious and sometimes even violent (all uncommon vices for her species) but who stands her ground against a genuinely-terrifying threat at the moment of truth and saves the city.
Knight in Sour Armor: Trixie. She demonstrates definite Heroic Spirit in this story, but has a huge attitude problem. She's also a strong contrast with the more conventionally-heroic character from the Mane Six to whom she is a Shadow Archetype, Twilight Sparkle.
But Liquor Is Quicker: Trixie and Piercing fell into bed together after a drunken celebration of their success. This didn't work out so well: Trixie was so disgusted at what they'd done that she fled Baltimare, at least temporarily putting an end to her friendship with Piercing Gaze.
Little Heroine, Big War: The larger conflict, between Celestia and Nightmare Moon, is decided by the Mane Six in the Everfree Forest, and all Trixie does for most of the story is keep a single neighborhood in Manehattan from rioting. In the end, though, by stopping the Night Coven from blowing up the fertilizer plants, Trixie saves Manehattan from a devastation which would have crippled the whole Equestrian economy and hamstrung the defense of the Earth down the line.
Magicians Are Wizards: Literally true in Equestria, because magic is common. Most stage magicians in that land are unicorn mages: the trick is to make one's magic look more impressive than it really is by employing stage illusions. Trixie is not only a fairly powerful mage for real but can pretend to do things well beyond her power level with the same sort of stagecraft Earthly stage magicians would employ (she favors misdirection, patter and pyrotechnics in her show). Her Super-Powered Alter Ego, the Alicorn Illusion, does something similar but from a much higher power level; some of her illusions are powerful enough to have real psychic effects.
Mentor Occupational Hazard: White-Beard the Grey died some years ago, leaving Trixie to carry on his tradition of stage magic alone.
Merchant City: The city of Manehattan began as a number of trading ports after the Ponies of the Three Tribes conquered it from the Minotaurs, and for a long time was a Free Republic under a confederation of Merchant Princes.
When Trixie is angry at her agent, Bottom Billing, for getting her the Tompkins Square gig when he (in her mind) implied she was going to do a Bridleway theatre, she obsesses over various horrible ways she could kill him. This is scarier than it would be for a human to have these fantasies, as the Ponies are not normally killers. However, Trixie is just joking with herself, as later events show that Trixie isn't a natural killer either.
The Manehattan Coven are casual killers who hate normal Ponykind, something which horribly impresses itself upon Trixie's mind when she meets them and feels their fear aura. The contrast makes it obvious the degree to which Trixie is far more grouch than literal psychopath.
Noodle Incident: Trixie once seems to have accidentally convinced an audience that there was a fire in a crowded theatre. The details are hazy but it ended with her fleeing a sheriff and an enraged mob.
Obnoxious Snarker: Trixie, frequently, the more so in her thoughts. Though being Trixie, often aloud as well.
Paralyzing Fear of Sexuality: Trixie may have this instead of true Asexuality, as she may be romantically attracted to Piercing Gaze. It's difficult to be sure, the more so because Trixie seems to be lying to herself about some of her emotions in that regard.
Ponies Of Mass Destruction: Both Princess Celestia and Princess Luna, which is why if Luna forces her into a personal fight, Celestia's plan is to lead her out into the wastelands, where they can both use their full powers without devastating any unfortunate towns that happen to be nearby.
Possibly also the Alicorn Illusion, since her City-Healing Wave of sanity restoration could probably be twisted slightly to produce mass insanity. Fortunately, she seems to be a nice mare, and wouldn't want to do any such thing. We hope ...
Post-Victory Collapse: After the Alicorn, Illusion, returns to dormancy, the Great and Powerful Trixie is left standing on stage, having not merely used all her magical energy but also consumed some of her own flesh to power more magic, and not entirely sure of what just happened. She tries to do her usual smoke-bomb exit, but faints from exhaustion in the middle of her last trick.
The Power of the Sun: Celestia's signature ability. Her strongest attacks are fusion beams and the ability to generate (and survive) a fusion explosion from her own body. The latter power is devastating, but omnidirectional, and she doesn't want to use it anywhere near an inhabited area for the obvious reasons.
Pride: Trixie's fundamental flaw. It's why she decides to go neither to Canterlot (where she could ask Princess Celestia about the Alicorn Illusion) or Baltimare (where she could renew her friendship with Piercing Gaze). She has to solve all her problems on her own, because she's The Great and Powerful Trixie.
Ragtag Bunch of Misfits: Princess Celestia wryly realizes on what a thin thread her hopes of defeating Nightmare Moon without a devastating battle hang:
Celestia (thinking): Now it's all coming down to my slightly-confused Faithful Student and whichever she can gather of the numerous candidate Element Bearers with whom I populated Ponyville. The magic should make her pick at least one of each of the five others, but ... I should have dispatched mechanized divisions, bomber wings, whole regiments of sunfire missile launchers. But I don't have any of those things. So I sent a librarian.
Reincarnation Romance: Princess Celestia hopes that the fact that Twilight Sparkle is the reincarnation of Luna's beloved Dusk Skyshine will prevent Nightmare Moon from killing Twilight and give the Element Bearers the time needed to use the Rainbow to purge Luna of the Shadow. It does.
Serious Business: Trixie's attitude toward her show; the Shadow Coven are willing to kill her to stop her performance, while she is willing to engage in a potentially-lethal magic duel to deny them this goal. Justified, because Trixie's life (and Cutie Mark) revolve around her art, while the Shadow Coven means to use Trixie's audience as a weapon to execute their Evil Plan (and in any case are hardly averse to murder). Also justified in the larger sense, since if Trixie had yielded they would have destroyed the city of Manehattan.
In the larger series, Twilight Sparkle. Both of them are powerful mages, but Trixie is a loner who succeeds (or fails) through her own skill and determination; Twilight succeeds by finding friends and working with them. Trixie is a Guile Heroine who puts up a cynical face but romanticizes all her situations, Twilight a Science Heroine who is sweet but highly-analytical. Twilight acts as a supremely-loyal agent of the Equestrian Realm, Trixie acts on her own behalf and cares little for the Realm (or really, anyone but herself and the few ponies she actually likes).
Piercing Gaze. Both of them showponies and stage magicians. He's male and middle-aged, she's female and young. He's wealthy and successful due to his ability to get along with others, Trixie is poor and struggling due to her lack of such ability. He's cool-headed and very sexually-experienced, Trixie hot-headed and almost a virgin. And yet they love one another, though in a very strange way due to Trixie's Pride.
The Nightstallion. Like Trixie he is a mage and a misfit in Equestria. He recruits the Shadow Coven, she works alone. He's evil, she's (mostly) good. He's murderous, she has a Code Against Killing. He wants to use his power for destruction, she to bring delight. He tries to destroy Manehattan, she saves the city. It must really burn him up that she is the one who is a fetal Alicorn.
Trixie explicitly thinks of the Nazgul when she sees the Shadow Coven. This is because a character who is obviously the same being as Gandalf has told her about the Nazgul in the first place.
The Show Must Go On: Trixie's credo as a performer, and thus a central pillar of her unusual code of honor. This is why she refuses to leave the stage when the Sun fails to rise, keeps on performing as buildings start burning and things exploding in the city around her, and faces down a coven of black magicians rather than give up on completing her show.
Spirit Advisor: White-Beard the Grey discarnated from Equestria a few years ago, but his power seems to be able to aid Trixie at key moments. For instance, when Trixie has been overcome by the fear aura
Suddenly she remembered White-Beard. No, felt him — the scent of him, a mixture of old stallion and beard, of mane and the tobacco he would keep smoking, no matter what anypony said. A great warmth went through her, a great courage, and her limbs seemed to regain some of their strength.
Stage Magician: Three referred to in-story. All three of whom are also actual mages, and the first two of whom are secretly Cosmic beings.
Stiff Upper Lip: Princess Celestia is determined not to panic her little ponies, and pretends to enjoy the party at Canterlot Castle, when she knows full well that in a few hours Equestria will be in a desperate fight for survival.
Sorceress-Queen: Princess Celestia. Proof of her benevolence is that, not only is she fully-intending to sacrifice herself to stop Luna if she has to in order to save Equestria, not only is she careful to leave a clear order of succession should that happen, but she even leaves orders for the leaders of the future resistance to make peace with Luna if she regains her sanity. In other words, she would rather see Equestria spared a destructive civil war than have her death avenged.
Superpowered Alter Ego: The Alicorn,Illusion, to which state Trixie has not yet fully Ascended but whom she can occasionally Manifest.
But what could happen here, at a local festival in the greatest city in the world?
Third-Person Person: Trixie is an extreme case, even more so than in canon. She refers to herself in the third person, even in her THOUGHTS, save when utterly overcome by emotion.
The War Room: Princess Celestia has built a well-fortified one under the Palace at Canterlot, though its protection has its limits. From here she issues her orders to try to ensure that something of Equestria will survive Nightmare Moon's coming should her Champions be unable to defeat her. The room gets described in greater detail in All The Way Back. How well-fortified? And what limits?
Celestia had specifically constructed this chamber to withstand the effects of the impact of gravitational singularities against the Palace proper. ...
The War Room could take a near-miss by a singularity, but no merely material object could withstand Nightmare Moon's full focused power. If necessary, Luna could have brought down the mountain itself in crashing ruin.
Thou Shalt Not Kill: White-Beard the Grey, worried about Trixie's possible future abuse of her abilities, impresses on his young apprentice not so much the moral wrongness but the banality of murder, because he knows that the one thing that Trixie cannot bear is to not be special:
Trixie, the old stallion was saying, you are truly great and powerful, truly clever, truly special. Think twice, think thrice before using your great power to kill. Wanton murder is what ordinary, dull, mundane creatures do. You are better than that! Your magic is to delight, to dazzle — not destroy!
So she lived on the road, by her wits, from hoof to mouth, from town to town? It meant that she was her own mistress, that no ignorant clod could tell her what to do, that she did what she wanted to when she wanted to do it, and for her own purposes.
World-Healing Wave: The Alicorn Illusion releases a city-sized one when she spreads her spectral wings to cover the whole island of Manehattan. It instantly heals all insanity directly caused by the Shadow Ponies.
Wrong Side of the Tracks: Tompkins Town is a classic Industrial Slum, with factories that process guano into fertilizer. Trixie is revolted by the smell, and the Nightstallion's evil plan is to detonate the fertilizer works, devastating the city.