Alright, let's get one thing out of the way. "The Lost Treasure of Griffonstone" is not filler. So far, the biggest complaint people seem to have about the episode is calling it filler. It's many things, but it's not filler. It's slow-paced and wastes a lot of time, but it is an episode that matters in the context of the series. In fact, this season has actually been rather light on filler. Aside from "Castle Sweet Castle", every episode has felt like an experiment, and they're all wildly different not only from each other, but from the episodes that came before. Of course, a consequence of that approach is that not every experiment will be successful. With that said, I have no idea why most people seem to like "The Lost Treasure of Griffonstone".
The main idea of this episode is that Pinkie Pie and Rainbow Dash need to go to Griffonstone to solve whatever problem the map has assigned for them. Given that this is only the second map episode, I'm not sure why they aren't questioning it at all, but hey, what else are they gonna do? Anyways, Rainbow Dash immediately expresses prejudice against griffons due to her bad experience with Gilda. Now, in "Griffon the Brush Off", Gilda was something of a complete jerk. You'd immediately think that not all griffons would be like that, right? Well, no. "The Lost Treasure of Griffonstone" attempts to explore the conditions that caused her attitude, and it starts by making the griffon kingdom decrepit and ruined. It's not entirely hard to understand why someone who grew up in this place would be something of a grump, but as much as the episode tells us that Griffonstone and its people are miserable, it doesn't go too much into the "why" of it all. Oh, sure, it never wastes an opportunity to show that the society is driven by money, but all the episode really says about why, exactly, Griffonstone fell is that the griffons "lost their pride". It's not a particularly compelling backstory, but hey, the episode's more about the "what" than the "why".
The thing is, this episode is heavy on world-building, and without that being on-point, what we're left with is sluggish and dour. That second quality in particular is a huge problem, because while the episode desperately strains for humour-and, in fact, boasts some pretty clever jokes-the depressing tone created by what we see and hear about Griffonstone mutes their impact, rendering much of the episode somewhat depressing. We see the return of Gilda here, but the energy of her previous appearance is gone, replaced by defeated grumbling. She just wants Pinkie and Dash to be gone, and while this isn't a situation where those two seem like pests, it's again depressing to see Gilda like this. She's a more interesting character here, to be fair, but a lot of the qualities that could be interesting are only explored at a surface level. It's not like the episode is overstuffed as is, so I genuinely don't know why they couldn't have used some space to flesh out Gilda a little more. Instead, we're left with not-particularly-entertaining banter between Pinkie and Gilda, and scenes of Dash just sort of going out and doing stuff. A surprisingly large part of the episode has Pinkie and Dash with no idea how to save Griffonstone, so we're left with the equivalent of exploring a town in a video game. It's just not particularly exciting.
The griffon society is immediately established to have a history of greed. I'm not sure if the griffon lore shown in the show has any parallels to the stories of actual historical cultures, but given that it's basically a planet of hats, I doubt it. In the episode proper, griffons repeatedly ask for money for the most trivial of things, which is amusing at first but quickly grows old. We already have the dragons for our greedy race quota, though. Did we really need this? If nothing else, I'll congratulate the episode on not going too far into a "greed is bad, friends are good" lesson, though there are implications of it. If it had gone there, then it would have been obnoxiously unsubtle, but instead the ideas pointing to that feel unfinished.
With all that, I already found this episode exhausting. However, it was when the episode started to pick up again that I started to get angry. Spoilers follow until the final paragraph.
In the end, Rainbow Dash gets stuck in a chasm while searching for this episode's mystical item. Pinkie Pie comes across her and looks for help, having been working on a fresh batch of griffon scones. Somehow, Pinkie manages to convince Gilda to go save Dash, because they were friends once. Gilda's motivations for this are kinda confusing, but the easiest explanation is that she's helping someone in need because she's not completely horrible. Gilda insists that this doesn't make her and Dash friends, which makes enough sense. If this episode suggested that you can still help people in need without being friends with them or even necessarily liking them, I think that would be one of the show's best lessons to date.
Instead, Pinkie Pie looks directly towards the camera and tells you, the person watching, that yes, Gilda helping Rainbow Dash does in fact make them friends. I mean, despite what I said previously, that is the implication, but it's not exactly hard to grasp. If Pinkie pointing out the subtext says anything to me, it says that we're too stupid to figure that out on our own. Typically, explaining your own subtext is considered very bad writing, and this is no exception. This isn't the last time Pinkie Pie breaks the fourth wall in the episode, with one time being during the delivery of the theme, just to add a little bit of winking at the audience. It's obnoxious.
Of course, Gilda winds up going through a forced reformation arc, and of the ones this show has had so far, this is my least favourite. It just feels far too rushed. They could have spent a lot more time on this instead of on Pinkie and Gilda's mediocre banter. Say, didn't Gilda blame Pinkie for Dash falling out with her? I guess she moved past that, because she displays no resentment for Pinkie. That might have been resolved in "Griffon the Brush Off", but I also wonder why Gilda seems more resigned than annoyed this time around. Irritated Gilda might have given this episode some more life. I find it interesting that the map sent Pinkie and Dash there, given that those two have a particular history with Gilda, but it doesn't really amount to as much as it could have.
Ultimately, though, the real kicker is the denouement. After Pinkie and Dash have made up with Gilda, she goes and gives one of Pinkie's fresh griffon scones to another griffon who she suggested was an acquaintance. The acquaintance indicates appreciation, which excites Gilda. Pinkie and Dash's cutie marks glow, indicating that they've solved the problem here. If it were just Gilda and Dash making up, that would merely be deeply underwhelming, but with Gilda giving the scone to the other griffon and a couple lines of dialogue afterwards, the implication seems to be that this is nudging Griffonstone in the right direction. Yes, apparently the magic of friendship will save a ruined civilization. Apparently no griffons have ever been friends before! Even ignoring the highly questionable idea of two ponies coming into a different civilization and potentially "saving" it by introducing their values, this is utterly asinine and reductive. Particularly in these circumstances, you'd think there would be at least some griffons forming bonds in the face of adversity, but nope. Am I expected to buy this? Besides, there's something condescending about the explicitly stated idea that ponies have friendship and griffons don't. Is it just griffons? We saw some dragon buddies in "Dragon Quest", so they seem to be able to form SOME kind of connection. And yet griffons can't? Sorry, I don't buy it.
I need to make it very clear that it's not just this handful of elements that bothers me about the episode. Even without the whole idea that griffons don't make friends, even without the mediocre worldbuilding, even without Pinkie breaking the fourth wall, this episode is still not enjoyable. The tone is depressing, and not much even happens for a good chunk of it. "The Lost Treasure of Griffonstone" seems to be trying to experiment with an episode reliant on worldbuilding, but it just doesn't have the execution to be anywhere near a success, and the infuriating elements I mentioned just push my feelings towards this episode into the realm of hate. I want to love season 5, but as much as I admire the ambition of it, aiming high just means that when you fall, you fall farther and harder. But hey, we're not halfway through yet, and at least leaving on a bad episode makes three-week wait for the 100th episode less of a daunting prospect. Let's just hope that one's something special.