Sweetie Belle has written, directed, and is starring in the school play, but she needs Rarity's help with the costumes. Rarity is very busy working on a special order for Sapphire Shores, the Pony of Pop, but she makes the time to produce three stunning outfits for Sweetie Belle, Apple Bloom, and Scootaloo. The Cutie Mark Crusaders perform their play to lavish applause, but when they go out to mingle with the audience, they find that their sisters didn't make it because they were helping Rarity. On top of that, the only thing anypony remembers about the play is the costumes. Sweetie Belle returns to Carousel Boutique, full of anger, and accuses Rarity of making the dresses too good on purpose. Rarity says she only did what she thought her little sister wanted, but Sweetie Belle has none of it, storming out in a huff.That night, Sweetie Belle is still angry and unable to sleep. While getting up for some water, she sees that Rarity left her door open. In her anger, she decides to sabotage Rarity's own work — namely, by removing a key stitch from the elaborate headdress which will be the centerpiece of Sapphire Shores' costume. Satisfied, Sweetie Belle goes back to her room and falls asleep, soon finding herself in a dream about accepting an award for her play. Even there, Rarity is able to ruin Sweetie Belle's happiness, raining and thundering at her until Princess Luna enters the dream to intervene.Luna says that she understands what it is like to have a sister who sometimes outshines her. Within the dream, she takes Sweetie Belle back to a birthday party which she remembers as a time Rarity deliberately upstaged her. Sweetie Belle had put on her best outfit to impress her party guests, but they ignored her and paid all their attention to the party favors that Rarity made. One filly even said that they didn't need the birthday girl when they had the birthday's girl's "amazing older sister," which sent Sweetie Belle back to her room in tears. However, Luna reveals that there was another side to the story: the guests were so bored with waiting while Sweetie primped and preened that they had nearly walked out, forcing Rarity to break out the favors early to save the party. Further, she had told all of them that the party favors were Sweetie Belle's idea.Luna then shows Sweetie Belle what had happened earlier that evening: Rarity was rechecking all of her work, second-guessing herself and becoming increasingly stressed, which Sweetie Belle admits she also does. Finally, Luna takes Sweetie Belle to what will happen if the sabotaged headdress is not fixed: Rarity is not only humiliated in front of Sapphire Shores, she becomes a laughing stock and a shut-in, obsessively rechecking everything and afraid to let anyone see her work. As she watches her sister descend into madness, Sweetie Belle can only beg for it to stop. When she finally wakes up, she rushes to Rarity's room to fix her mistake. But Rarity has already left for Canterlot!With the other Cutie Mark Crusaders in tow, Sweetie Belle heads for Canterlot, making it to Sapphire Shores' dress rehearsal. Rarity is just about to show off the headdress when the Cutie Mark Crusaders enter through a window, grabbing the box the headdress is contained in and fleeing. Sweetie Belle manages to get out of sight just long enough to fix the stitching, with the unexpected help of the real Princess Luna. Rarity finally catches Sweetie Belle, who explains everything and apologizes to her sister.Sapphire Shores is getting uneasy about the weird delays, but her concerns are instantly swept away when she sees the final piece, which has the image of a dolphin stitched on the front. Neither she nor Rarity can tell how Sweetie Belle knew her lucky animal, which swims with her in her dreams. (Luna, off to one side and out of sight, nods at Sweetie Belle.) Rarity then apologizes for being so caught up in her work that she missed Sweetie Belle's play, and asks for an encore performance. Sweetie Belle admits that the play wasn't that good, and the costumes were the best part.
Tropes present in this episode (YMMV tropes go here):
Ageless Birthday Episode: Actually averted this time around. Sweetie Belle's birthday shown in the past was specifically her fifth one, thereby making her at least older than five. It's also evidence that ponies age at a somewhat similar rate as humans.
All Cloth Unravels: Rarity's headpiece for Sapphire Shores is held together by a single key stitch.
Always Someone Better: After the misunderstanding at Sweetie Belle's fifth birthday party, she learned to "never try to shine with her big sister around".
Bad Future: Princess Luna shows Sweetie Belle a potential future where, should Sweetie Belle's actions go unchanged, Rarity will become a complete laughingstock in Equestria's fashion community and become an insane recluse.
Body Horror: Part of the Nightmare Sequence has Sweetie Belle's hooves stuck to the floor as Rarity is about to unveil Sapphire Shores's headdress, preventing her from warning everypony that she sabotaged it. Her hooves stretch and even show holes in them similar to a changeling's.
Before the nightmare sequence, Luna says to Sweetie Belle, "Go see what the future holds if you fail to rein in your worst instincts, as I once did", explaining the results of Luna's envy that banished her to the moon for a thousand years.
The starfield Luna and Sweetie Belle traverse when moving between dreams matches the astral plane Twilight met Celestia on when Twilight underwent her ascension.
Chekhov's Gun: Dolphins appear throughout Sweetie Belle's dream, with her swimming with them in the transition to the present, and a dolphin design appearing on Sapphire Shores' stage during the Bad Future portion. Guess what Sapphire Shores' lucky animal is.
Comically Missing the Point: When the Crusaders consider how they should behave toward the audience after the play, Sweetie (the clumsiest of the three) suggests "gracious", Scootaloo (the most arrogant) opts for "modest", and Apple Bloom (the most sassy) goes with "classy".
Sweetie Belle has adopted Twilight & Cadence's de-stressing technique from Games Ponies Play.
Several background fillies and colts, including some that first appeared in "Twilight Time", make brief appearances as foals in Sweetie Belle's fifth birthday party flashback.
Control Freak: Sapphire Shores has perfectionist tendencies, which puts a lot of pressure on Rarity. Though possibly justified, as a lot of famous musicians and performers have to very meticulous about details in their appearance and performances (mostly to avoid upsetting "that one guy who will notice if something's off").
Cosmetic Catastrophe: To primp for her fifth birthday party, Sweetie Belle applies a giant, irregular smear of lipstick.
Damned by Faint Praise: Noteworthy tries to give Sweetie Belle a complement about the play, but he can't remember a single line from it.
Noteworthy: I liked some of those lines you said. Sweetie Belle: Oh really? Which ones? Noteworthy: Uh, I don't really remember, but you were wearing a pink taffeta dress with lots of chiffon when you said them!
Do Well, But Not Perfect: Sweetie Belle wanted Rarity to make good dresses but not jaw-dropping amazing ones, though she only makes the complaint because her play fell flat by comparison.
Dramatically Missing the Point: When Sweetie Belle learns that the costumes Rarity made were praised over the rest of her play that she wrote and acted in, she assumes Rarity purposely overshadowed her work, rather than consider her own less-than-spectacular talent. She comes to realize her mistake at the end.
Dream Weaver: In addition to entering Sweetie Belle's dream, Princess Luna is able to guide the dream to help Sweetie Belle realize the possible consequences of her ruining her sister's work.
Eye Twitch: Rarity in the last of the Bad Future nightmare as she's huddled in the middle of her ruined boutique.
Face Plant: Happens to Sweetie Belle when she's trying to walk in her dress during the flashback to her 5th birthday.
Getting Crap Past the Radar: Rarity says, "Without this key hidden stitch, [the headdress] is just a..." then says, "I'm trying to think of a nicer way to say, 'big bummer'." But we all know the word she was searching for was the one that rhymed with "stitch".
Luna apparently knows a thing or two about sewing, and Sweetie Belle says she likes show tunes.
Sweetie Belle writes and directs an entire play, as well as acting in it, indicating a budding interest in the creative arts.
Apparently Sweetie Belle resents Rarity for being better. This puts her Big Sister Worship from previous episodes in a whole new light.
Human Ladder: The Cutie Mark Crusaders do one to try to get into Sapphire Shores' studio, but it didn't go very well.
I Need to Go Iron My Dog: When Sweetie Belle storms in and glares at Rarity, the rest of the Mane Mares use "take that moment to relax" as an excuse to leave the room so the sisters can talk in private.
Innocently Insensitive: Everypony praising the play's dresses, unknowingly, hurts Sweetie Belle's feelings, as nopony paid any real attention to all the other aspects of the play.
It's All About Me: Sweetie Belle before the CMC perform their play. It may be true that she took the lead on this project, but she couldn't put on the play without her friends' help.
Sweetie Belle: I worked so hard on this play. I wrote it especially for the three of us. I directed it, I'm in it, I made the costumes—it's just that this is really my time to shine doing something completely myself!
Moment of Weakness: Sweetie Belle's undoing the hidden stitch, done when she was furious with Rarity despite knowing how important it was.
My God, What Have I Done?: Sweetie Belle first feels this when she didn't learn the complete story behind the fifth birthday incident with a Heel Realization. She feels it even stronger at the end of the nightmare over ruining Rarity's reputation.
Nice Hat: Part of Apple Bloom and Scootaloo's costumes. Rarity has a whole selection for Sapphire Shores and her band, with a particularly extravagant one for Sapphire herself.
Nightmare Sequence: The first part of Sweetie Belle's dream before Luna arrives. It returns for the final part of the dream interlapping with a possible Bad Future for Rarity.
Sweetie Belle is genuinely surprised to learn that Rarity suffers from the same insecurities she does.
Princess Luna also compares Sweetie Belle's relationship to her sister with that of her own.
Out-of-Context Eavesdropping: At Sweetie's fifth birthday party, her guests were all distracted by the cake and party favors that Rarity handed out, so Sweetie thought Rarity was deliberately upstaging her. As Princess Luna shows her later, the guests were in fact bored waiting for Sweetie Belle, and Rarity was just trying to keep them interested until Sweetie Belle arrived.
Background Filly: Who needs a birthday girl when you have the birthday girl's amazing big sister! [Sweetie Belle runs away, in tears.] Rarity: Oh, no, no, no! All of these things were Sweetie Belle's idea! I just...assisted with the execution.
Out of Order: Aired as the 19th episode of the fourth season, despite being the 20th produced.
Plot Parallel: Luna briefly contrasts Sweetie's situation with Rarity as hers with Celestia.
Poor Communication Kills: In the present of the episode, the fact Sweetie Belle didn't tell Rarity about this play weeks ago leads to needing her to rush it and get her own work done in time. In the past, Rarity failed to explain why she passed out the cake and party favors early at Sweetie's fifth birthday party, so Sweetie Belle just assumed she did it on purpose and refused to discuss it further.
Popcultural Osmosis Failure: Apple Bloom and Scootaloo mention a couple of Sapphire Shores' song titles, one of which Sweetie Belle mistakes for a snide comment about her sister. Sweetie Belle explains that she doesn't know Sapphire Shores' pop songs because she prefers show tunes.
Prehensile Tail: Apple Bloom hooks her tail over a pennant banner and suspends the weight of all three Crusaders from it, using the banner as a zipline.
Reset Button: Averted. When Sweetie Belle says "I wish none of this ever happened," Luna shows her a way forward to resolve her dilemma and face the consequences of her actions.
Ridiculously Cute Critter: You thought regular Sweetie Belle was adorable? Five-year old Sweetie Belle manages to be even cuter.
Sanity Slippage: Rarity in the Bad Future nightmare, the whole embarrassment over the head dress leads her to obsessively double check everything to the point she eventually can't even make any dresses anymore.
Scare 'Em Straight: Rather than simply chew Sweetie Belle out for her sabotage of Rarity's Nice Hat, Luna instead puts her through an eye-opening Nightmare Sequence to show her just how awful and misguided her behavior is/will be if she persists.
Schizo Tech: Sapphire Shores' security guard is wearing an earbud.
Rarity asks, "What in the wide wide realm of Equestria" similar to the way Slim Pickens says, "What in the Wide Wide World of Sports" in Blazing Saddles. Twilight previously said a similar line in "Feeling Pinkie Keen".
The Violin chord played during the dream sequence as they descend through an ocean sounds very similar to a piece played during another oceanic descent.
Stealth Pun: Luna mentions that she knows how Sweetie feels to have a sister who outshines her. She explicitly uses the term "outshines". Now keep in mind who her sister is.
Stop Helping Me!: In-universe example. When Sweetie Belle tries to explain to a security guard that she's not trying to see Sapphire Shores because she's a fan, Apple Bloom and Scootaloo both cheerfully exclaim that they are. ("Not helping.")
Suspiciously Similar Substitute: The two bitchiest fillies at Sweetie Belle's fifth birthday party — the one with lavender hair and the one with glasses — act like they could be younger versions of Diamond Tiara and Silver Spoon, but they don't have the same colors.
Tooth Strip: Averted during Sweetie's Nightmare Sequence, specifically when she falls into Rarity's mouth. Rarity's teeth are drawn individually.
Tough Love: Pretty much how Luna's operating here. Scolding Sweetie would be way too easy, showing her what her actions could lead to is much more effective.
A Tragedy of Impulsiveness: Sweetie Belle pulls one thread out of the headdress in a fit of pique. It turns out to be the thread holding the entire thing together, setting off the chain of events which ruins Rarity's career.
Traveling at the Speed of Plot: You have to wonder about how often and fast the trains are from Ponyville to Canterlot if the CMC are able to arrive in time to stop Rarity from giving Sapphire the sabotaged headdress, on a indeterminably later train than the one Rarity took earlier in the day. Especially after the train detoured through a desert for some reason. Possibly justified, as we see Rarity watching Sapphire and her troupe rehearse for what may have been a rather long time.
Who's on First?: When Sweetie Belle mistakes a Sapphire Shores song title ("Serves Her Right") for an insulting comment directed at Rarity's future being ruined.
Wilhelm Scream: Heard as the crowd flees the rainstorm at the award ceremony near the start of Sweetie Belle's dream.
Ye Olde Butcherede Englishe: "Forsooth and anon, I cometh forthwith and posthaste," begins Sweetie Belle's play. Major Stylistic Suck for anyone who knows anything about Elizabethan linguistics: forsooth means "truthfully", expressing an opinion; anon means "shortly"; cometh is third person conjugation; forthwith means "immediately", contradicting anon; and finally, posthaste means "with great speed". So, basically, Sweetie Belle says, "In my honest opinion, very shortly now, I comes immediately and quickly," as she's casually strolling onstage.
Yet Another Christmas Carol: Except without the Christmas (or Hearth's Warming) element. Princess Luna plays the part of all three ghosts, showing Sweetie Belle her past, the present, and the future in a dream.
You Know What You Did: Sweetie Belle blames Rarity for deliberately upstaging her, both at her her disastrous fifth birthday party and at the just-finished play. But when she confronts Rarity, she fails to explain what she's blaming Rarity for, leaving Rarity completely befuddled about the source of Sweetie's sudden outburst.
Your Door Was Open: Despite having no luck with Sapphire Shores' security before, Scootaloo and Apple Bloom are able to run right in once Sweetie Belle gets in through the window.