Note: Expanded from my forum post. Credits to comments by @BornAgainBrony, @Truffles, and @Ittoni for the review.

This whole episode is packed with lots of smaller details, which on rewatch go a long way. One of the first instances is this exchange between AK and her former fans.

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Older Fan: On page 531, it says Daring Do kicks puppies!

Filly *voice breaking*: She does?!

AK: What?! No!

At first, it looks like a throwaway line that Groom Q.Q. Martingale threw in there. But in the beginning of Act 2, that concerned filly returns to her book signing, where we see more of this exchange:

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Filly: So Daring Do doesn’t kick puppies?

AK: That was one time! Accidentally.

During my rewatch of the saga last month, I assumed it referred to kicking away the wild cats, one of them a housecat, during Daring Don't. But those weren’t accidents; she tried to defend herself. Despite her initial denial, she finally admitted to not only accidentally kicking a puppy, but didn’t put it in any of her books.

Why does this small exchange matter?

1. The Daring Do Series is a series of autobiographical events, but because she’s trying to sell stories to children as well, she sanitizes, alters, and omits things that might disinterest or repulse the audience. She edits each book to make the stories more sellable and sells the books as fiction. For a long time, that tactic worked; each "character" has become memorable, and there's a huge Daring Do fandom out there. Now it's starting to backfire.
2. It opens the door for the possibility of more laying beneath to the whole Daring Do saga. Remember, the series is written in third-person limited perspective, every adventure in Daring’s point of view. Groom Q.Q. Martingale's opens that point of view, painting her stories in a more negative light while still making sense.
3. More importantly, Caballeron’s response becomes more credible to the general audience. Yes, he’s scheming to steal the Truth Talisman of Tonatiuh, but because of the editing of her own book, she opens things up for him to explain his own side and sprinkle truths both big and small that she didn’t tell. As omissions and inaccuracies big and small add up, doubt clouds the Daring fanbase's head, which Fluttershy and the little filly represent. Innocuous details like the flower being the wrong color now implicate she has something to hide.

During that exchange, Dash busts back in to warn A.K. that Caballeron is bringing Fluttershy along to Tenochtitlan. During the frantic warning, she looks around to see if anyone was around (not seeing the filly), just to see if no one is sneaking around. Like Dash herself, A.K. Yealing forgets about the child, revealing her original identity as Daring Do to the filly's shock and delight. Despite the growing scandal, some ponies still idolize her and want to grow up to be just like her.

Another one comes in Fluttershy's first scene in the Tenochtitlan Basin. Notice his twinkling highlights and small smile as she tames Ahuizotl's jungle cats. For the first time all series, he shows sincere appreciation for someone other than himself. Usually greedy and selfish, he watched firsthand how much someone's selflessness and unconditional caring mattered. He brought her over to trick her; despite carrying that trickery throughout, his plan began to both crack and evolve.

Yet, that crack didn't quite begin there. After Caballeron scolded at Rogue for almost poisoning himself, what does she do? Take out her traveling picnic with apple juice to Caballeron's surprise and share her lunch with them out of appreciation. Rather than snub her, he and his henchponies accept her generosity. Had this not happen, Caballeron's appreciation for Fluttershy from that point forward won't make sense.

From the very beginning, Fluttershy was convinced that there's more to the Daring Do saga than what A.K. Yearling told through her books, even though she witnessed Caballeron and Ahuizotl firsthand commit bad actions. Talking personally with Caballeron while in the bookstore only made her more curious. So, was she gullible and naive? Absolutely. However, her naivety is much more believable compared to buying a too-good-to-be-true rag doll from Flim and Flam during Best Gift Ever, and one key moment shows she isn't that gullible:

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Fluttershy: Daring Do did have a lot of artifacts on her shelves at home. But didn't you try to sell them to the highest bidder?

This indicates awareness of the events and an expectancy of Caballeron to try to explain the problem. So how does he respond? With a plausible alibi surrounding a museum that closed down from lack of funds. Daring's long history of storing many sacred artifacts on her shelves, destroying temples older than the Royal Sisters, and thus the homes of many animals (something she cares about deeply) also invited questions on her behalf. While she listened to and questioned him, he explained his lies while remaining grounded to Equestrian reality, and his book while under Martingale has enough credentials to sway many ex-fans. Additionally, she was very well aware throughout that Martingale was Caballeron, talked to him as if he was Caballeron, and never reacted at all when he reveals his identity to her.

Also, Fluttershy never wavers her unconditional kindness regardless of any circumstance. During the entire expedition, she stayed true to her embodied Element of Harmony and exemplified it wherever she went. In each scene, Caballeron and his gang slowly show appreciation for it, both subtly and obviously. Beyond the examples from above:

1. At the closure of the first expedition scene, Biff, Rogue, and Withers smile in thanks for Fluttershy.
2. At the base outside of Tonatiuh's pyramid, Caballeron yells at Biff for suggesting to take a shortcut, and Biff feels disrespected by him despite being second-in-command. Fluttershy reassures him that he will and she believes in him (which happens inside the central room).
3. Once they reach the top, Withers relaxes under shade, unaware that he was under an active, dangerous flyder hive. Instinctively, she whispers to stay still and called the flyders away for just a moment so he can escape. Again, Dr. C smiles appreciatively.
   
   On an unrelated note, Tonatiuh is the Aztec god of the sun, and the only way to enter his temple is to place a sacred relic in a pedestal once the sun reaches its apex. If intentional, clever tie-in to its mythology.

Inside the temple, Caballeron tricks Fluttershy to getting the Truth Talisman of Tonatiuh (I'll get back to it in a sec), and once she retrieves it, lava spurts out. Previously, Caballeron and his henchmen were somewhat cowardly and only went after the treasure. If something bad was going to happen, they'd leave it behind. That doesn't happen here. Instead, they instinctively knock down a totem pole, and Caballeron rescues Fluttershy from certain death. Again, they didn't have to do this, but they chose to rescue her and save her. Yes, they retrieved the talisman, but because of her kindness, they returned the favor.

Fluttershy's naivety in this scene, however, is problematic in two areas:

1. Throughout almost all of Daring Doubt, Dr. Caballeron was very competent. However, his use of false despair to convince Fluttershy to fly up and steal Tonatiuh's talisman wasn't convincing whatsoever and lazy. By falling for his bad acting, she crosses from being just gullible into becoming dumb.
2. Fluttershy reveals to having no idea that Caballeron planned to trick her the whole time. If Fluttershy knew beforehand he was scheming yet went along, it subverts the idea that she was too gullible, instead showing she knew what she was doing. OTOH, it also makes her really reckless, implicating she knows Caballeron poorly acted, yet helped him steal the talisman and put her own life at risk. Right after he reveals to lie to her, he soon reveals that he valued her kindness and friendship, a smaller subversion in and of itself and downplays unneeded drama, but it also lessens the weight of his small change of heart.

Caballeron revealing his lie through the Truth Talisman could've gone either way with varying implications. The canonical path, as stated before, shows her unconditional kindness, especially after her ignorance towards Angel's needs fueled the conflict, but it made her look way too naïve and made his eventual understanding of FS's kindness at the end feel too lucky. OTOH, had Fluttershy showed controlled kindness, then you risk repeating the unfortunate implications of controlling Discord's channels of communication in the form of "kindness" from Keep Calm. Personally, I prefer the innocent path here, but it could've showed a more nuanced degree of taking elements from both.

Now to focus on the other side, Rainbow Dash was written much better here compared to 2, 4, 6, Greaaat. To echo @BornAgainBrony, Daring Doubt is a shining example of giving Dash negative traits without making her out of character or miserable. Yes, her rush to judgment was written in the wrong, but at no point does Dubuc demonize her for her black-and-white "good guy, bad guy" assumptions. With the allotted time given to her, Dubuc rightfully justifies her prejudices.

1. Daring Do and Rainbow Dash are both very good friends and better confidants. Whenever she's about to publish something new, she delivers a copy to her two weeks in advance. The entire main crew, especially Dash, is trusted by her to keep her identity a secret.
   
   BTW:

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   Dash: "That's supposed to be a secret!" [grunts, throws book across room]

   >RM6 out her in Fame & Misfortune
   >episode retcons the journal again
   
   Not the first episode to handwave this atrocity's existence!

2. As a result of Daring and Dash trust each other, they exchange information and secrets. If something goes wrong, Daring knows Dash will be there to try to help. Here, that's exactly what happened.
   
   When Dash first sees Groom Q.Q. Martingale, she immediately recognizes him as Caballeron despite a much more complicated disguise, an immediate improvement of Daring Done. Watching Fluttershy buy into Caballeron's story was a major shock; she has every right to be upset and urgently warn Daring about what he was after and why he manipulated her like that.

3. Quote

   Rainbow Dash: So if this Talisman is so important, why didn't you already save it? You said only a Pegasus can get it, right?

   Daring Do: Yes, but the temple traps are far too dangerous to face without a map. And maybe even with one.

   Rainbow Dash: [gulps]

   No one can argue how abrasive and pushy she was here. But Caballeron began yet another scheme, decided to tag someone along to unknowingly help him retrieve the Truth Talisman to get rich quick, and took her to a temple with very dangerous traps (one in which FS got caught in minutes later). Her worries are perfectly justified. Imagine if Fluttershy got hurt — she wouldn't forgive herself for not interfering sooner!

4. Once Caballeron admitted through the talisman that he lied, she got right in his face, as any good friend would. But then he admits through it his and his henchmen's gratitude for Fluttershy's kindness and generosity, Dash's edge immediately dissipates:

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   Rainbow Dash: Didn't see that coming.

   Ditto.

Speaking of lines, the dialogue during the escape (especially those influenced by the truth teller) was top notch, and some of the lines were really, really funny. Some of the best are:

1. Caballeron fighting with the talisman, finally relenting to reveal he still held onto Lapis-Lux's diamond.

2. Quote

   Daring Do: A truce until we escape? How can we trust you?

   Dr. Caballeron: *touches talisman* I cannot lie. *lets go* Now, all together!

   Clever, clever.

3. Quote

   Rainbow Dash: *under talisman's trance* I'm gonna need the deluxe spa package after this adventure. *normal* That doesn't leave this temple! *throws to FS*

   Perfect timing to sneak in a clever "Day" Off callback, eh?

Now, let's talk about the thorn peaking out from the pond.

Ahuizotl has earned a reputation in the Daring Do books as one of the most memorable villains within the fanbase. In reality, both he and Daring have been massive archenemies, even though Dr. C's an even bigger one. Several times, he has tried to kill Daring Do in order to prevent her from taking relics throughout the Basin. In Daring Don't, he searched for ones himself — the Rings of Scorchero — to trap Tenochtitlan Basin in a massive heatwave, only for Daring and her friends to foil his plan. One of her latest books involved Ahuizotl heading to Somnambula to separate the Doomed Diadem of Xilati from the Tiara of Teotlale (a.k.a., the Sister Crown Relics), and Daring raced the clock to steal it back and return it home before a cursed night was cast over the land and Somnambula was sunk beneath the sand.

Daring Doubt shifts things a bit, at first accusing Daring of getting by his jungle cat army and then attempting to steal Tonatiuh's talisman, even though he has no idea that Caballeron and Fluttershy are inside. After they escape, we don't see him again, but once we do, he's furious. Not just an evil furious. He was at his angriest throughout the show's history. Despite his history as a villain, who can blame him. It was safe and secure, and from his reaction, he clearly did NOT want it stolen.

And he shows the knowledge of Tonatiuh's temple by waiting for them at the main exit, and his anger really takes over. He wanted to retrieve that talisman and play no games, going so far as to cornering them in a dead end and ramming into it, threatening to hurt them and trap them under the temple rubble until they return it.

At this point, Daring accidentally gives Fluttershy what may be the solution:

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Daring Do: Ahuizotl won't give up until he catches us. We have to find another way out!

Think about this. They steal the talisman, and he becomes supremely upset when he catches them. She's the only one astute enough to understand that something was missing, this being why he got so mad, and the only way to solve it was to confront Ahuizotl himself. Dash justifiably assumes that he's "just a bad guy," but FS realizes that the world sometimes operate so one-dimensionally.

On one hand, Ahuizotl's explanation for being ferocious and violent has some merit, something both @Ittoni and @BornAgainBrony explain in their posts in the episode discussion. Throughout the series, Daring and Caballeron have been taking artifacts throughout Tenochtitlan Basin, and in doing so, many ancient pyramids have been destroyed. Whether it's in the name of profit or protection, they're still stealing from them and displacing them, which each carry massive consequences. Ahuizotl is given charge to protect not only the basin, but also the artifacts of these same ancient beings. For those who watched the series throughout, this explains quite a bit why he and his crew of Aztec ponies searched for those rings, began the ceremony inside the dark tower, and came so close to beginning that heatwave within the basin. If he completed his plan, then neither Daring nor Caballeron would rob the temples again without potentially deadly consequences. Also, I see why the episode establishes him as a guardian in the first place; he's sly, territorial, knowledgeable, and old enough to know every nook and cranny of Tenochtitlan Basin from the back of his three hands. But thanks to Cabby and Daring's rivalry, he's caught in the crossfire and at risk of being replaced; Tonatiuh's talisman being the tip of that sun ray.

On the other, it overlooks a very specific piece of continuity, which was ironically referenced in Act 1: Why did he travel to Somnambula, allegedly separate the Sister Crown Relics, put hundreds of lives at risk, and cause Daring to go on one of her most dangerous journeys? What made him decide to apparently team up with the Wild Bunch Gang to steal Xilati's diadem from where it belonged? None of this was answered, which it should've. He did many things both in the main and secondary canon that we would consider evil, and this would easily be his worst. Given how Daring Doubt tried to explain his actions and make us at least understand his position, you can argue one of two answers.

1. By forcing Daring and Caballeron to go to Somnambula, there's a chance that both of them would get stuck there and sink under the ground, which would keep every relic in Tenochtitlan Basin safe. With them out of the way, he won't have to worry so much about them grave-robbing anymore.
2. Since this plot is about clearing up misunderstandings by listening to others, there's also the likelihood that he was caught in the crossfire. The gang chased her through Somnambula after she retrieved the Doomed Diadem from them and apparently Ahuizotl. Could Ahuizotl have been trying to recover it too, only to be caught in the crossfire? Given how the books are in her perspective, it makes his motives look more sinister than she believed.

Theory #2 is more in character to the portrayal of his rivalry with Daring and Daring Doubt's dismantling of Daring's limited perspective of the journeys. But without a clear answer, we can only guess what truly happened and must rely on headcanon to fill in the gaps as well as reviewing little, overlooked details from previous episodes. An episode with this important a moral and with a very gray perspective of humanity must be treated with respect. Is it? I argue yes, but if others don't, I can see why. Ahuizotl's apparent trip to Somnambula may not have been that important in Daring Done, but when observing the arc as a whole, this plot point is now crucial in overall scope. Unfortunately, this resolution fails to deliver any explanation, much less a decent one, creating a massive plot hole in a worldbuilding idea that never fully delivered. Therefore, Daring Doubt doesn't adequately explain why Ahuizotl acted so violent this whole time.

Fortunately, this episode's resolution isn't completely unsalvageable. Review all of the reformations over the seasons, from Diamond Tiara to Starlight to Sunset. What do they all have in common? In some way or another, they all change their ways, even if their personalities don't. What happens here isn't a true-to-FIM reformation or redemption, which — again — @BornAgainBrony points out well. Nobody agreed to anything other than a truce related to Tenochtitlan Basin. As long as neither of them steal treasures or destroy the temples, Ahuizotl won't come after and threaten them. But that doesn't mean their feud won't continue anywhere else. Daring Do will still hunt for treasure and store them however she can so no one else can destroy or desecrate them, while Caballeron's greed remains (only without one sidekick ). What this episode establishes is how despite being enemies, neither of them truly have any moral high ground. No true good or bad guys exist in the reality of Daring Do; Fluttershy has that wherewithal to deliver an objective perspective to help put them all on the same page and listen to one another.

Plus, @Truffles points out an important distinction between Ahuizotl's explanations and Garble's reformation from 9A. Throughout the series, DHX established Garble as a petty, stereotypical teenager with a lust to pick on Spike whenever possible, and will threaten anyone if he doesn't get his way. However, Sweet & Smoky tries to introduce a more sensitive side to his personality by being close to his younger sister Smolder, who's more open to his quirks and talents. Thanks to his past actions, his secretive side's hard to sell, even after he opens himself up to save the baby dragons from freezing to death inside their eggshells. Daring Do's triangular feud here lacked that key position of listening from the get-go, and creating a series of limited-perspective books that prop up Daring's status as a hero only invited extra questions about the lore. Until the climax, nobody ever asked Ahuizotl about his behavior before, evident by how taken aback he was to FS's question. Daring's urgent line in trying to figure out an escape route and Fluttershy's awareness created a plausible out for a truce.

This review, though, won't be complete without praising the ending. How hilarious is it that after trying very hard to avenge his losses over the years, his decision to become a best-selling author himself would be his most successful path. The way he presents himself to the audience makes him credible, and patting his hair as he reads is a nice touch.

All in all, Daring Doubt dares to deconstruct the world of Daring Do. At times, it works. At times it doesn't. But overall, the good heavily outweighs the bad. I like it a lot, and rough edges aside, it's nicely done. It's a good episode and the best one of the Daring Do arc.