Xenilla for Spacegodzilla. In this case, the readers aren't the fans who came up with the nickname; the author is. Notes state that Tarbtano thought the official name sounded too ridiculous and he felt silly typing it; along with not wanting to confuse newcomers to the Godzilla franchise by having one character being another character's name (Godzilla) with an adjective.
Fandom Nod: Several reader OCs make appearances in the story, and the Big Good turns out to be the living incarnation of the Tree of Harmony, a popular fan creation.
Follow the Leader: Most crossovers between Kaiju properties and MLP were done mostly in the sense of taking a kaiju film and putting in ponies in place of humans, reusing film plots; and/or throwing the kaiju into Equestria fully formed but otherwise just as pure monsters. The Bridge was the one that either started or popularized the ideas of using a wholly original plot with transformed kaiju being given alot of characterization. Post-Bridge, several stories began using very similar ideas.
My Little Destroyah technically did the Kaiju-to-Pony transformation first and had a lot of dialogue coming out of its titular character, albeit it's scale was much smaller and it still mostly used Godzilla vs. Destoroyah's plot for it's latter run.
Gateway Series: The series gained a considerable readerbase among readers who were either just G-Fans or just Bronies/Pegasisters prior to reading, getting many to try out the other series. Many of the Godzilla film streams Tarbtano either hosted or linked had attendees admitting it was their very first kaiju film. It also served as this for some to fellow fanon series The Shimmerverse.
After an illustration of Controller 011 was released, several fans immediately speculated that she was pregnant at the time of her death, until Tarbtano explained that what looked like a belly bulge was really her big, poofy sleeve.
Xenilla a.k.a Spacegodzilla was given two possible origins in the films by being born of Godzilla Senior's cells floating into deep space by way of either Biollante or Mothra. Most canons and merchandise which give a defined origin use Biollante so many readers assumed the same. Later chapters showing his origin and affected biology however make it clear that in Bridge canon, Mothra was the vector.
Milestone Celebration: Around the fic's 2nd year anniversary, Tarbtano and Faith-Wolff released an animated Q&A video.
Schedule Slip: The animated Q&A video was meant to celebrate the fic's 2nd anniversary, but was released a month late due to technical difficulties, which included losing footage and having to re-record it.
He seems to have embraced this label after posting several very confusing puzzles in his blog posts that were teasers for an upcoming story arc.
And then there's this blog post listing events that he claims will happen at some point in the story, the majority of which are things the readers have been asking for, but some of which are so outlandlish that they don't seem possible. Given that it was posted on April Fool's Day, it's been generally accepted by the readers that at best, there are some actually events mixed in with others that are only there as a prank.
And now he's giving the readers an algebra, biology, and paleontology quiz to figure out a clue to a teaser. Either Tarbtano is a troll or a deranged grad student.
Comes to a new height with the spin-off "Sound of Thunder", where he caught almost everyone by surprise by using the mirror universe from the IDW comics, despite previously stating he wasn't going to do so for the main story. To his credit, he didn't say no to using it in a spin-off and it did line up with a previous statement that the spin-off's cast would meet Bridge proper's roster (in the form of their Mirror World counterparts).
A blog post by the author gave some details about the original plot. It was going to be a short story taking place in Manehattan with a heroine caring for a depowered and shrunk kaiju. When another, more malign monster enters Equestria, the first one transforms to fight it off before they both are teleported back to Earth. Basically the first act of Digimon: The Movie with Godzilla characters and ponies. Candidates for the starring kaiju ranged from Godzilla Junior to Anguirus or possibly Rodan, with the villain role taken by Spacegodzilla or King Ghidorah. Vinyl Scratch, an original character, or Applejack were all considered for the Equestrian heroine role.
While the story as a whole was greatly expanded, some elements of the original ending sequence did work their way into the story proper. The build up of fight between Anguirus and the dragons in the campground does closely resemble the Digimon plot, with key elements like the malign giant monster (Garble) destroying a bridge, and the smaller good monster (Anguirus) growing in size to save two bystanders from falling debris.
Godzilla, Mothra, and Rodan's Equestrian forms were originally going to be Earth Pony, Alicorn, and Pegasus respectively. In the final story Godzilla became a unicorn, Mothra a changeling queen (though she did get an alicorn disguise), and Rodan became a gryphon.
Originally, Gamera was going to be one of kaiju sent to Equestria as an Earth Pony, but he was later replaced by Anguirus. Some leftover elements of this remained in the final story, such as Anguirus being befriended by a young filly (since Gamera is a Friend to All Children).
Scenes from Anguirus' battle against Garble and the dragons and Rodan landing on Garble were going to be illustrated, but Faith's pictures looked kind of awkward and were scrapped.
Monster X was originally going to turn into a Kirin in Equestria. Instead because of the weakened barrier, he's just shrunk.
Faith drew a rough sketch of Monster X regrouping with Gigan in Equestria and Gigan was fully visible, but the finished product had Gigan hidden in shadows to make it easier to draw.
The picture for Derpy's introduction was slightly different and originally showed both of the princesses in frame.
Xenilla and Blade Dancer's manes were going to have a more Greco-Roman style.
Blade Dancer was supposed to be a one-time-use character but fan adoration and new ideas on how to use her made her evolve to a reoccurring cast member.
The Halloween Special was going to have a picture of Gigan's fight with Mane-iac, but then they decided to do one of Mane-iac flirting with Gigan because it would be funnier.
Destroyah's teeth were going to be a lot longer and nastier looking, resembling Sabor from Tarzan.
The Holiday Special was originally going to have Godzilla and friends enter the Equestria Girls realm before it was changed to Monster X and Irys.
The concept art of Monster X's human form originally had him with claw-like nails and his face was not covered.
The Holiday Special was going to have an image of Irys and Sunset Shimmer's hug, but Faith found she's not good at drawing vehicles (the scene took place at the threshold of a bus).
The Mother's Day special originally was going to have a Downer Ending with Azusa finding out about Godzilla Junior's supposed death in the first chapter with Dimension Tide sucking him and five other kaiju into a black hole. This was cut to avoid any Darkness-Induced Audience Apathy and give a upbeat ending to what typically amounts to a happy holiday.
The Father's Day Special was going to star Godzilla's father and Tarbtano even started a rough draft of it. Then he decided since the Mother's Day Special starred Godzilla's mother, he should mix it up and have it star Celestia and Luna's father figure instead with Starswirl.
The author planned for Queen Chrysalis to infiltrate the Crystal Empire at some point before changing his mind and coming up with a different plan for her eventual appearance. The infiltration idea was instead given to a revived King Sombra.
The Youtube videos that accompany some chapters would have been fully animated instead of still images, but Tarbtano and Faith lack the time, resources, and expertise to do this.
Tarbtano noticed that his planned Chapter 29 (which would have been called "Henshin, Henshin!!!") was a little short, so he combined it with Chapter 28.
Tarbtano bounced around which Siren would start bonding with Monster X before choosing Aria Blaze because she has the least amount of headcanon of the three Sirens, so it would be easier to work with her personality without upsetting the fans.
There was going to be a chapter called "Siren Dame, Dragon Knight". Because it was over 31000 words long, it was split in half, into "Siren Dame" and "Dragon Knight", with "Siren Dame" ending on one of Tarbtano's classic cliffhangers.
Tarbtano originally planned for Orga from Godzilla 2000 to be in the cast. He would be a tragic figure because he started out as an alien scientist who wanted to conquer Terra to give his people a place to live, but then his transformation into a Kaiju warped his mind. His plot would involve trying to stabilize his mutations and avoid losing his mind, learning empathy along the way.
The OC's like Blade Dancer and Blueberry Frost were going to be very minor characters, but the positive fan reaction to them led to their roles being expanded.
Similarly, there were not going to be any romantic pairings, but the positive fan reaction to Ship Tease moments led to Tarbtano changing his mind. In a very early draft of future chapters that considered giving Godzilla Junior a love interest, Princess Celestia was originally considered as Tarbtano felt Princess Luna pairings were often poorly done.
In the scene where Blade Dancer steps in to stop Junior from attacking Xenilla, Junior would have been releasing so much heat that her sword melted. Tarbtano changed his mind when he realized if Junior was hot enough to do that, Blade Dancer's body would catch on fire. Tarbtano thought such a cool moment wasn't worth breaking the willing suspension of disbelief.
The song Azusa sings in Chapter 32 was meant to be one from Godzilla vs. Mechagodzilla II, but Tarbtano says it was hard to find the lyrics and when he finally did, he realized it didn't fit the situation, so he instead had her sing the traditional Edo Lullaby, which fit better.
The Generation 1 Tirek would have appeared as a villain, until "Twilight's Kingdom", which revealed the Generation 4 Tirek, aired. Starlight Glimmer would have been an early antagonist, but Tarbtano wanted to wait until Season 5 was over to learn more about her. Starlight's older sister Moonbeam was then created and used as a minor antagonist.
In the scene where Gilda confronts Rodan, Tarbtano considered having Gilda bring up the fact they were both gryphons during her attempt to turn him against Rainbow Dash, but realized the argument would be pointless since Rodan is more connected to the ponies and isn't even a real gryphon anyways.
Tarbtano explained during a Q & A that originally Xenilla actually was intended to be the Big Bad of the story, which then transitioned into Grand King Ghidorah being the main villain, before he finally settled on Bagan. The intended Final Battle to the second version was later reused for the Climax Boss fight with Grand King Ghidorah.
Tarbtano said in a blog that in Chapter 38, he was going to write out Princess Melpomene and Hymnia's kidnapping and rape, but there is no way to have a scene like that without pushing the fic into an M rating, felt he couldn't write it on a clean conscience, and he was disturbed trying to even think about it. It was changed to Electra vaguely hinting about it with later character appearances and mentions confirming it did happen.
Grand King Ghidorah was going to debut in Equestria in a native form, either a dragon or an Alicorn, but Tarbtano couldn't think of who would empower him to transform. It was changed to him arriving in his true form.
Chapter 44 was originally going to end with Lea, Twilight, Flash, and the Equestria Girls successfully escaping X unscathed. After regrouping at Sunset's place, Lea would then decide to call in Junior and Anguirus as backup. X would then contact Bagan and ask for Gigan, Megalon, and Irys as backup. A revised ending had them almost escape X, only for Gigan to appear and come to his teammate's aid, capturing Twilight.
Both Zilla and King Kong were considered for the story's cast. While they were both added to the world's canon with the Television Series' Zilla Junior and Legendary Picture's King Kong appearing in spin-offs, they were kept on Terra.
"Legacy of Everfree: A Hearth's Warming Tale, Finale" had three alternate endings, one where Wysteria survives and decides to keep her secret of being Gaea Everfree from her children, one where Wysteria lives long enough to carry the survivors out of town before dying, and one where Harmony takes Wysteria's comatose body into her realm in the hopes of reviving her one day. There were also two scenes that were cut, one a comedy scene where Wysteria wakes up and does her morning routine until her husband revealed she had been in Gaea Everfree's form the whole time, and one where the Windigos discover Gloriosa Daisy is the new Gaea Everfree.
Word of Gay: Tarbtano says at least one of the Mane Six is a lesbian or bisexual, but says it is not important to the situations and will not really be focused in the story.
Word of God: The spelling for Monster X's alternate form varies depending on region, with Keizer or Kaiser Ghidorah being the most common. The in-story spelling of Kaizer is an attempt to reconcile this disparity by combining the two most popular spellings.