So finally, after getting seemingly outshined one time too many and enraged by it, Sweetie decides to get even on Rarity and sabotages a key headdress piece for a series of costumes Rarity is making for her important client, none other than Sapphire Shores. Going to bed satisfied, Sweetie Belle at first has no regrets for this choice.
Until Princess Luna shows her the error of her ways...
Anyway, the episode's major theme is one of sisterly bonding, much like "Somepony To Watch Over Me" earlier in the season, but this time focusing on Sweetie Belle and Rarity, what is probably the show's favorite for this theme. Most of the episode is focused on Sweetie Belle, who has to learn that not only is Rarity not deliberately trying to outshine her, but that it wasn't really as bad as she was making it out to be, and that lashing back wasn't the way to resolve it. This leaves Rarity as the episode's means-to-an-end, and thus the developing is left mostly on Sweetie Belle and not Rarity, who remains mostly the same as before. A bit of a pity, because I would've liked to see Rarity get something out of the episode as well too.
However, given the story the episode tells, it is perhaps understandable as to why that did not happen, which I'll get to shortly. To begin with, the episode is built on a somewhat obvious Dickensian display of "past, present, and yet to come" events to teach a lesson, so much so that the moment you catch onto it, the episode becomes rather predictable. Some fans have already started to criticize that cliche use of storytelling, and probably rightly so, but at least one can't overlook the fact that the episode does use it to teach an atypical lesson associated with this style of storytelling, and it isn't deliberately obvious about it, like many other cartoon shows that make use of this same tactic. It tries to be subtle about it, so to make the parallels seem merely incidental. It doesn't quite succeed, but the attempt is appreciated nonetheless.
Besides, I can overlook the cliche if only because it results in Luna appearing with a key role in the episode, which I will NEVER say no to (unless it is a spectacularly bad episode, which MLP has not yet done during its whole run thus far, IMO) and better still, grants Luna a chance to be a bit more open than usual about her dark past. It has not escaped my attention that since her return, Luna (and Celestia too, incidentally) has been very tight-lipped about said past, and not without understandable reasons. No doubt she wants to move past all of that and not be stuck dwelling over events she can no longer change. In fact, she still pretty discreet and indirect about it even here in this episode, but the fact it comes up at all strikes me as something important to note.
The last time Luna visited one of the CMC in-dream, "Sleepless In Ponyville," it was basically just to tell Scootaloo to face her fears. This time though, it's much more personal for Luna, because she can relate to Sweetie Belle's situation, having been precisely there before and as a result made some mistakes she's lived to regret (Nightmare Moon) and now is here to try and keep Sweetie Belle from doing something actually frightfully similar. In so doing, this gives a rare insight of what was no doubt going through Luna's mind via Sweetie Belle when Luna no doubt made her own choices to lash back at her own sister's perceived upstaging, eventually giving rise to Nightmare Moon. Since the details of this time has been left in the dark for so long, I can't help but latch onto this insight for the clues it provides, and also gives one a better ability to see the whole matter of Nightmare Moon from Luna's side for a change. For from solely her perspective, it wasn't entirely unjustified. But like Sweetie Belle, Luna probably didn't stop to consider the whole story, and ultimately made mistakes more than just her had to suffer for.
With that in mind, you can't blame Luna from doing all she can to keep other ponies from so foolishly making the same mistakes. She's already been there. And probably wouldn't wish it on anypony else.
Furthermore, it also suggests to me that whatever it was that brought on Nightmare Moon all those years ago, it probably wasn't done through one great event like is sometimes suggested to be, but rather a slew of smaller events that ultimately culminated in Nightmare Moon. It started with something small, something petty (like, in Sweetie Belle's case, sabotaging a headdress) and built from there the longer the situation went unresolved until it blew up and became something as drastic as Nightmare Moon (this makes me wish more than ever that the show's crew would hurry up and give an in-depth, canonical, retelling of the rise of Nightmare Moon from the beginning, because it's clear to me there's quite a tale that could be told there if they'll just do it. Maybe for their next pseudo-movie release? Would rather see that than another Equestria Girls, to be honest).
This isn't, of course, to say that Sweetie Belle was at risk of becoming a Nightmare Belle (or whatever you prefer) had she been allowed to pursue her petty revenge on Rarity and probably was never in any danger of anything like it. That's not the point, though, the point is that Sweetie Belle would've regretted it in the end, but by then it no doubt would've been too late, and would've left a lot of damage for probably more than one pony that would probably never be totally resolved. That's what the episode is really about. It's Luna's way of proving this to Sweetie Belle, and that this one action literally could lead to so much sorrow, and her attempt to try and prevent it entirely before it was too late, again so to spare Sweetie Belle that grief Luna no doubt knows all too well.
Problem is that Luna can't just tell Sweetie Belle all of this, because Sweetie Belle's too irate (and she's seriously angry too, perhaps angrier than we've seen her get in a long time) to listen. Which leads me back to the episode's Dickensian methodology which now seems much more justified to me after going through all of that. Cliche as it was, showing Sweetie Belle the dangers and consequences of her actions was perhaps the most effective way to do it, and kudos go to the writers for perhaps recognizing that. It's possible even that the cliche really was only incidental initially in its writing, though I doubt it. Point is that the display of "past, present, and yet to come" events to teach a lesson the episode employs is perhaps more fitting and works better than you might want to give it credit for. And gave the animators a chance to have fun and be creative portraying the Equestrian "dreamscape" as I've heard many fans call it and was overall fun to watch.
So, maybe a better episode than you first thought, eh?
Still, there is one downfall to this episode's tactics and that's simply the fact that because of those tactics, it had a lot of material it needed to cover in a very short space of time. The writers handle it pretty well and use their time very well (better than in a lot of other episodes, in fact, where said episode wasn't even in as pressing a need for it) but despite their efforts, the episode does come out somewhat rushed, particularly towards the end. Some details get overlooked, though thankfully mostly just minor ones. Some examples I thought of: how did the CMC pay for their train ride to Canterlot (it's been well-established now that there is a fee), and better still, how were they able to board without a guardian looking after them without drawing attention, as past events suggests they are still young enough to require one (I count Spike as a guardian for their unplanned train ride to the Crystal Empire in "Just For Sidekicks" and he feels mature enough to be one to me whereas the CMC do not)? In fact, it seems like they all got a "get-anywhere-in-Equestria-without-question-for-free" pass because save for Sapphire Shore's studio, they seem to be able to get pretty much anywhere with ease in this episode without any pony hardly batting an eye at it. Then there's also the wish for Rarity to learn something to that I mentioned earlier. They're pretty minor issues, and given the time constraints, not important to explain, but still, I would've liked an explanation, no matter how simple, to them if it were possible.
Still, I'm quite pleased with this episode, and would personally change very little about it. Luna was probably my favorite character in the episode, and I rather like her subtle and behind-the-scenes manner of addressing a problem, unlike Celestia, who strikes me as more the kind who'd get involved more directly (or just send Twilight to do it *eyeroll*). It fits her character pretty well. Though this episode does give an instance of where we see Luna active both in the day and night. Does she ever sleep? Or maybe she does the dreamwalking while sleeping herself? Inquiring minds wants to know! Mostly mine!
Also, we get a clue as to the age of the CMC in this episode for the first time; they're older than five in pony years. Since their current age is notably a few years afterward, I would guess that, at the very least, they're two-to-three years older than that. So...seven or eight in pony years? Though personally, I'm leaning closer to ten. Give or take on which one of the CMC it is, of course as they probably aren't all the same exact age (like how we know the Mane 6 aren't all the exact same age either)
I would also guess that when Sweetie Belle turned five, Rarity had not yet moved out (because the house the party is portrayed taking place in is quite clearly the family home and not the boutique) but probably would soon do so.
And one more thought on the episode's dream sequence; I figure that the "bad future" Luna showed Sweetie Belle stopped after the sabotaged headdress was revealed, and that the rest with Rarity going loco was Sweetie Belle's imagination being permitted to envision the worst from there. Because let's face it, that bit was a touch far-fetched.
Who attends a play and enjoys it only for the costumes?