Early-Bird Cameo: Bravado turns up for a single chapter in Griffon's Goblet where he is perusing his own adventure that has nothing to do with Daring's current one at the Summit. He helps Daring get the key needed to steal back the eponymous Goblet from Ahuizotl's minion in exchange for helping him get his hoofs on a satchel of unknown contents. It's implied later to be one of the pieces of Star Swirl's staff that he ends up losing and has to help Daring recover later on.
It's believed that Mistress Spark's background appearances were intended to be Early Bird Cameos that never came to pass.
Early-Installment Weirdness: Because the author didn't know it would be a series yet, Daring Do and the Sapphire Stone is the only book not to explicitly include supernatural elements; the Sapphire Stone is never even hinted to have any supernatural powers. It is also the only book where Daring goes on the expedition completely by herself, she does not own Calypso yet, and it is surprisingly short, making it seem no less epic but set in a vastly smaller world than what is established later.
Earn Your Happy Ending: Tinker's Seal. It took several near-death experiences, an invasion of soulless soldiers, more Artifacts of Doom than you can shake a stick at, and an explosion that could have taken the Everfree Forest off the maps, but the artifacts were secured, and Krastos and the Assembler were finally taken down.
Eldritch Abomination: The Great Intellect in Curse Of The Yeti, The Great Beast of Chaos mentioned in Alicorn's Shadow. Krastos, Smooze, Nightmare Inti and the Assembler from the Expanded Universe.
Enemy Mine: Several Expanded Universe works involve Daring Do and Ahuizotl teaming up to stop another villain from destroying the world with an Artifact of Doom, like in Amber Of The Smooze and Scepter of the Chaos Beast.
Bravado and Daring (who normaly compete with each other) have one at the start of The Staff Of Star Swirl Daring and Ahuizotl have a canonical one near the end of the book. It lasts all of five minutes before he double crosses her for his own aims. Even Daring acknowledges that it was stupid to trust him to any degree.
Daring: Yeah...Should have seen that one coming.
Equine Resources: The Assembler, who uses whatever flesh it's gotten to create new members for its army, and recycles existing constructs for raw materials as it sees fit.
Everything's Better with Monkeys: The eponymous Shrine of the Silver Monkey has a primate based theme going for it. Including a giant gold statue of a multi-armed... bipedal thing. It then comes to life to stop Daring. Scary stuff.
Expanded Universe: One of the more expansive of Equestrian literature. Originally, Expanded Universe works were not required to be in-canon with each other, but with increasing collaboration between authors, and especially after the massive work that was the Tinker's Series, this line is becoming increasingly blurred. Furthermore, information revealed in the Tinker's Series has been adopted as background canon for EU works, even for authors who don't write sequel material to it, because many of the original authors had given their input to that series.
Expy: Platinius from Griffon's Goblet is Mane Retief in a less comic setting.
The Diamond Dogs in Trials of Unity are Expies of the three Diamond Dogs in J.R.R. Tackien's The Miniature.
Fuergott, from the Expanded Universe book Burning Heart has been dubbed by displeased fans as a ripoff of both Inferno and Sweeney Trot, in that she is a fire-based villain with a tragic backstory. Other fans claim that a few similarities do not a ripoff make.
Sterling Silver, from Cloudfall Conspiracy, has been accused by some critics as an Expy of Sebastius Mareton.
Face Death with Dignity: Assuming it actually died, the Assembler, in Tinker's Seal. It recognizes the leyline's detonation as being (potentially) fatal to Krastos, and simply considers his duties to be fulfilled.
Fanfare: The music for one of the plays got fillies humming it for years.
Fantastic Nuke: In Tinker's Seal, we have Daring blowing up a Leyline by feeding it Chaos Magic then setting off a large explosion next to it. Leylines are normally extremely stable, the use of Chaos Magic to destabilize one only really exists in theory.
The Colt Leader's death by My Skull Runneth Over in Universal Cracks, as her access to the Multiverse overloads her ability to control it, causing countless thousands of Alternate Realities to flow through her.
Felony Misdemeanor: The crazy pony insisting that no pony should play ping pong may be on to something....
And the Assembler to Krastos, in the expanded universe.
Food Porn: The three paragraph long description of the grasses, herbs, and wildflowers in the Marengeti certainly got this tropony drooling!
And that flower garden in Purloined Stone.
Foreign Queasine: The griffon territories use a wide variety of meat-based dishes, which is sickening enough for most Equestrians. However, wild horse meat is considered a delicacy, which as the closest non-sentient relative to ponies, makes it particularly Squicky.
The chilled horse brain scene can be nauseating for first-time readers.
Fortune Teller: Mirror Dreams in Alicorn's Shadow. She tries to coach Daring through the academic portion of dream interpreting after her first encounter with the titlar Alicorn's Shadow, but alas...
Though Daring can at least make educated guesses regarding the visions after the second and third encounters, thanks to Mirror Dreams's tutelage.
She also pops up again later in the series, most notably at Canterlot University. Her showdown with Nagridge was EPIC.
The Fourth Wall Will Not Protect You: A part of The Cove of Candles has a plot twist turn out to be that certain events of the book may not have been real, an illusion cast by Blackmane. The thing is, the book never tells you which parts were and weren't grounded in reality.
Friendly Rival: Bravado, a dark grey Spanish pony falls under this heading. Like Daring, he is a treasure hunter. Unlike Daring, though, he sells what he finds to the highest bidder. There are no hard feelings between the two, however; they often help when the other is in danger. Subtle hints have been dropped in several books that suggest there may be more than just a rivalry between them... Several fans have latched on to this insinuated relationship, creating fanfictions with scenarios that range anywhere from unrequited love, torrid romance up to outright marriage.
Gambit Pileup: Holy horseapples, Griffon's Goblet. Daring wants to get the goblet for a museum, Ahuizotl is playing Hawkwings like a string bass in order to take over the griffons, Platinius is desperately improvising to prevent an international incident, Nimbusbeak wants revenge on Hawkwings for backstabbing her for a promotion, and Copperbeak's Nightwings are stirring the pot everywhere.
Gas Whole Victim: Gas Whole, the Colt Leader's draconic abuser, enjoyed tormenting her relentlessly. When he eventually threatened the Colt of Smooze, she broke him, flayed his scales, eviscerated him, and used his blood as a slide down the mountain side.
GASP: in the original canon series the main characters rarely do this, although minor or supporting characters who are caught off-guard do.
Getting Crap Past the Radar: Having a magical lock that can only be unlocked with your horn could be innocent by itself. However, the following line of dialogue HAS to be intentional.
Just hurry up and stick it in already!
I see you're using your pay as wisely as ever, sister dear.
Gondor Calls for Aid: When Herpy manages to mobilise a whole group of past characters including Bravado, Outback Jack, Desert Rose, Mirror Dreams, and Swinn and Dell in Temple Of Nightmare Moon. Even Tabula Rasa provided the directions, and Starlight lent them her airship... and Coco Pie provided snacks!
A similar reunion occurs in Tinker's Seal, with all of the above and more rallying together to hunt for Steam Whistle's inventions.
Gone Horribly Right: The Colt Leader's Draconic abuser claimed he only abused her the way he did to make her strong. And she was. Strong enough to kill him at least.
In 'Tinker's Seal, both Mareton's beating at the hooves of Claddie and the Blanks getting an impromptu lesson on firearms courtesy of the Marksmare are covered up by the book's most heartwarming moments.
Heh Heh, You Said X: No matter how dangerous the situation may be in the Cove of Candles, Daring can't help but inwardly snicker whenever Blackmane so much as mentions the poopdeck.
Hero of Another Story: Every time Bravado shows up except for Star Swirl's Staff he is always doing something completely different from Daring, they always end up trading favors and (usually) part ways with a little flirting. Derring is also implied to be having her own adventures while not working with her sister.
A major theme after Mareahnee falls in Caverns of R'ni.
Hijacked by Ganon: Daring Do and the Cove of Candles was originally played up as featuring a completely new antagonist, the ghost of Blackmane. Guess who shows up two thirds of the way through as the real villain? This ends up happening in every book except Legacy of Nightmare Moon and Spear of the Windigos.
Played With in ''The Staff Of Star Swirl, Daring spends about half of the book thinking that Ahuizotl is the one she's working against only to learn a third party is the real enemy. He reclaims his role as villain after pulling a Enemy Mine for all of five minuets
By the time Ring of the Marengeti came out, they didn't even bother pretending anymore. Ahuizotl's minions show up in the very first chapter, and even on the cover.
Hoist by His Own Petard: Inti. It seems that, even imprisoned in the Moon, Nightmare Moon should not be underestimated.
In Ring of the Marengeti, Ahuizotl's habit of using the artifacts in his doomsday plots literally comes to bite him in the flank as he is the first target of Sobek.
In Cloud-Held Eternity, after Daring returns to her normal age and saves Shifty Gaze from the crumbling architecture of Cloudyon, he tries to throw her back into the Fountain of Youth, only for an expectant Daring to dodge and cause him to fall in himself.
He only got found out when Professor Storm Talon, finally getting around to having his leg re-adjusted after mis-aligning it in Temple of Nightmare Moon, pointed out that he could taste fresh horse meat in the cupcakes and while as a griffon that's not a problem, it was supposed to be illegal to sell meat-based products in Equestria without clearly labeling them (most meat-based foods being pet food anyway).
And when they find Trot preparing to carve Lightning's corpse, Storm Talon draws a knife. Sweeney tries to use the Staff fragment, which liquifies his flesh and muscle.
Impostor Reinie Has No Accent: In the Young Daring Do Expanded Universe book Return of the Fire of Friendship, Lady Blue-Blood noticed that Lady Dove did not tap the rigging with a forehoof thrice for good luck anymore, and investigated. King Mayhem got wise to her investigation.
The Incitatus: King Hammerhoof in Platinum Crown. He is a clear expy of the historical Incitatus...
Dride, the drone leader of the changeling swarm in the semi-final Blood Diamonds book, is paranoid, incompetent, petty, and has random migraines and violent fits, with only some of his problems being caused by his Blood Diamond's thrall.
In the Blood: Darrin is so far the only member of the Do Family to display no interest in archaeology. Even then it's heavily implied in The Trident of the Seaponies and at the start of The Trials Of Unity (where he refuses to partake forcing Derring to ask Daring for help) that it's mostly out of bitterness from the Parental Abandonment.
In Medias Res: Daring Do and the Quest for the Sapphire Stone, the first novel of the series, starts off with, "As Daring Do trekked through the tropical jungle, the wet heat sapped her energy and slowed her every step. If only she could escape this oppressive atmosphere and fly up into the cool blue sky, but her crash-landing in the jungle had injured her wing and she was grounded for a few days. Few days. It might as well be a few months. Or a few years!" The reader only finds out who she is, why she was on a plane, why she is on this mission, and her relationship with Ahuizotl through flashbacks over the course of the next few hundred pages. But before exposition, we get ACTION!
In Memoriam: Gusty Lulamoon was given a mention in the introduction to Tinker's Seal, with a short biography written by her college friends and longtime housemates J. Thunderlane Hurricane and Ember Roundup, who described her as a great writer and a great friend.
Beatrix Lulamoon is slated to provide one in the upcoming Alicorn Amulet
Insistent Terminology: Outside of Equestria and other equine-held lands, most creatures use the more obscure -"body" suffix as opposed -"pony", as in "anybody", "everybody", or "nobody".
Also, in books where Changelings are featured as characters, they use their equivalent of these words with the even more obscure -"ling" suffix, such as "everyling" or "anyling". This becomes a plot point in Return of the Fire of Friendship, as Lady Dove's ingrained and habitual use of these words tips Daring off to the fact that Dove is the disguised Changeling.
Insufferable Genius: Derring-Do is damn good at what she does. Unfortunately, she'll never skip an oppotunity to let you know it. (especially if Daring Do is around)
Ironic Echo: At the start of Griffon's Goblet, Daring states to her class that most archeology is done in an archive, looking through tomes and scrolls because "there is no large checkmark indicating the right place." Guess what she finds on the large tile sealing the Knight's tomb?
A heart-wrenching one happens in the Blood Diamonds novel Never Forgive Me: As Kimmy was originally to be Kimono of Harmony Sentai Ponyranger but changed at the last minute, she used Kimono's Catch Phrase, "This... is why I live out of town." When Daring finds her delusional, she's just been advising an imaginary Bad Liar about supposed "welcome signs" that she tells Daring are obviously a present. She then comments the Catch Phrase.
Killed Off for Real: It seems that this was supposed to be the case for Ahuizotl, after Daring Do shoots him in the head with a cannon in Temple of Nightmare Moon, especially given his conspicuous absence in Legacy of Nightmare Moon. Fan outcry resulted in his return in Shrine of the Silver Monkey.
Seems to have been finally played straight at the end of Ring of the Marengeti, considering he was Sobek's first victim, there's no mention of him after the beast is defeated, and it's the last printed book of the Core 16. Of course, given the nature of the Expanded Universe works, it's likely he'll still be making plenty more appearances in the future, possibly with some Lampshade Hanging.
Played more straight with Inti, although he wasn't exactly killed. It's possible that he could return, but the lukewarm fan response to Legacy of Nightmare Moon makes this unlikely.