WARNING: Rambling, self-absorbed bullshit ahead. Proceed with caution or just skip to the end for the good bit (ie, the soundtrack).
The Moonstone Cup started out as a Star Trek crossover.
I used to do fanwriting many, many years ago (don't bother looking for any of it, it's all under a different nick and long gone) and decided to come out of retirement to pony pony after being inspired by FredMSloniker's wonderful semi-horror anthology The Monster Mash. I had written a couple of fluffy one-shots (they're posted under my account here) and decided to try my hand at one of the adventure stories I have so very much enjoyed.
At the same time, I'd been watching a lot of Star Trek (blame Netflix), and had just finished watching the FiM season 2 opening, so an idea formed of a story wherein Q would bring the post-Nemesis Enterprise into Equestria to team up with Discord, the Princesses and the Mane 6 against an ancient menace that was attempting to destroy both universes, The Devourer.
I wrote two chapters of this and then remembered why I hate crossovers. In retrospect, even as bad crossovers go it was conceptually pretty awful. I had pulled in Seven of Nine and two rather lame OCs for the Enterprise's replacement senior officers. The explanation as to why Q needed the Enterprise was pretty sad. It just goes on from there. It was bad and no one will ever see it.
All that being said, much of the establishing stuff in Ponyville and some of the concepts (especially using earlier-gen MLP continuity as a white-washed version of "real" history) still seemed interesting to me. Indeed, much of chapter one of The Moonstone Cup, other than a few pieces of dialogue, is copied almost verbatim from the Star Trek crossover. I had a second concept of a magic tournament and decided to develop that. Once I came up with the idea of Trixie summoning an alternate-continuity Trixie as part of the qualifiers, I was pretty much set on writing this.
There are plenty of things I would do differently if I did it over again. First, I would write the climax and ending first. The last handful of chapters, less than 10k words of a 60k word story, took nearly a third of the writing time of the whole thing because it was just so hard to tie everything together. I'm not 100% happy with how it all worked out, either; in particular, I think everyone saying that Najstariot's attack on the city and her final defeat with the Elements was sketchy and didn't really seem to fit is exactly right. I never did figure out what to do with it so I finally decided not to do anything and just let it stand.
Second, for my next big anything I will get some solid editing help. The editing on TMC was very spotty and some of the help I got was from some very nice volunteers on ponychan who I didn't really get a chance to develop a working relationship with, so my responses to their edits were maybe not what was being looked for.
Third, I don't think I'll release any multipart stories to the public until I've got a good few chapters under my belt. I feel bad for editing out from underneath people as I went (some of the comments on the early parts don't make sense anymore because they're talking about things that were changed).
So, thoughts on the story itself. Being that it's essentially a shounen anime tournament arc, it's not exactly deep material, but I tried to put across a few core concepts, especially responsibility and the effects of history. A thread that ran all through the story was how the war between the Sisters, a thousand years gone, was having a direct effect on the lives of people today. There were also sprinklings of other history (the various treaties between the races, the decline of the ghuls, etc); I wanted it to be very clear that the past was very much still alive.
As for responsibility, Twilight and Najstariot both, I think, exemplified what I wanted to say there. Twilight had all sorts of responsibilities thrust upon her, first as a national hero (responsibilities that were thrust upon her and her friends in the series itself), then as a celebrity and finally as a very powerful being in her own right. Especially with some of the arguments (Rarity getting upset at Twilight over the fire, Rainbow Dash and Twi arguing about whether Twilight was taking the competition sufficiently seriously) I wanted to put across not just the Spider-Man lesson (with great power comes great responsibility) but in fact that everyone has many simple responsibilities (responsibility to treat her friends with respect, responsibility to herself to do her best, etc), whether we want them or not.
Najstariot was also an emblem of responsibility but in an opposite direction. I wanted her story to be a classic tragedy, a great person brought low by a character flaw. In Najstariot's case, it was fear and resentment that brought her low by causing her to reject her responsibilities as the queen of dragons, as a tournament organizer, and as one of the world's great powers. Twilight discarded all responsibility to anything but power when she touched the storm, and then Najstariot let her fear and anger take over completely and threw away the last of her responsibilities in response, attacking Canterlot and her old friends and allies.
In the end, though, The Moonstone Cup was not a philosophical treatise, just a stab at popular fiction and an attempt to entertain myself and anyone who would be good enough to pick it up. I'm glad people enjoyed it.
Cultural and world notes
I expanded rather heavily on the world shown in the series. In particular, when I was originally developing the idea and the basic concepts were coming together I decided it wouldn't work if there were just ponies competing, and so I took some rather radical action in developing the dragons, gryphons and diamond dogs into races on equal footing, both magically and culturally, with the ponies so that I could have a wider competitor base.
The most drastic development is the ghuls. The ghuls are intended as a synthesis of the Diamond Dogs and the G1 Grundles; the core of my idea was essentially that the subterranean canine people were the oldest sentient race (the Grundles being an unfortunately racist portrayal from the bad old days when ponies didn't interact much with the other races) who had long ago passed the height of their power, were dying off and had been doing so slowly for thousands of years, their place in the world essentially supplanted by earth ponies. Ghuls have specific innate magic that allows them to commune with the earth, and ghul sorcerors in particular can "speak" to gems to create general magic through them, an ability once shared by the whole race. Civilized ghuls have coloration similar to jackals. The Ghulic language as written in a few spots in the story is Arabic.
The dragons here were developed long before Dragon Quest happened, and I decided not to try to integrate the Great Migration; it will figure some into the sequel, however. Dragon society responded to the threat of the Windigos very differently than any of the other races; any sort of interpersonal harmony is essentially impossible for dragons, so instead there was a diaspora. Ormsreich is the seat of draconic power in the world, and by tradition any dragon outside Ormsreich proper is essentially an embassy in its own right. Dragon society is largely anarchic; Najstariot (prior to being egged) held de jure autocratic power over all dragons everywhere, but even before her partial withdrawal after the war she had a very claws-off approach. Dragons "breathe" magic (hence the various shrieks of spellcasting). The Draconic language written in The Moonstone Cup is real-world Macedonian (a Slavic language mutually intelligible with Bulgarian and, to a lesser extent, Serbian).
I developed the gryphons somewhat, but to a lesser extent, I think, than the dragons and ghuls. Gryphon civilization is organized around the aeries, towns and cities constructed at the peaks of mountains. Each aerie is essentially an independent city-state led by a chieftain or king, with disputes or major decision-making done at mass assemblies of the leadership of some or all of the aeries. Gryphon magic was until recently oriented either toward military or esoteric purposes, with the result that gryphon summoners, who could serve both as warmages and as shaman, have the most developed magical schools and training. Gryphon magic is based on chants and using the beak and claws as channeling foci. Gryphon language is unpronounceable by normal ponies (or humans).
Much about the war between the sisters is explained in the story and I'd like to save the rest for later; suffice to say here that it was a bloody affair that lasted several years. In Moonstone Cup continuity, the G1 special "Rescue at Midnight Castle" is essentially a whitewashed version of the real atrocities that occurred at Luna/Nightmare Moon and Rubedo/Tirac's hooves.
The last (and, of course, most important) thing: The soundtrack.
Main Theme: Iron Maiden - Rainmaker
Qualifying Rounds: Orgy - Opticon
Vs. Shahnaz: Monx - The Signs
Vs. Gianna: Marty Friedman - Fuel Injection Stingray
Vs. Trixie: The Cruxshadows - Dragonfly
Vs. Zlatan: yelworC - Bloodwhited
Vs. Amarok: Intrigue - Orbina
On The Clouds: Samael - Infra Galaxia
Final Battle Against Najstariot: Dragonforce - Cry Thunder
Some Bits of Incidental Music
The Road To Canterlot: The Rogues - An Dro (sadly, I couldn't find a good Youtube link)
Graveyard Theme: Mortiis - World Essence
Award Ceremony: Tchaikovsky - String Quartet No. 1 in D Major, Movement 2
Each chapter in the sidestory was named for a song that was more or less Trixie's personal theme music for that chapter: