One morning, helmed by Scootaloo, the Rainbow Dash Fan Club begins a hearing to officially declare Rainbow Dash as the most awesome pony in all of Ponyville. When Snips objects, preferring to call Rainbow Dash the most stupendous pony, a short argument unfolds, eventually resulting in an anonymous suggestion of "superultraextremeawesomemazing" by a certain cyan Pegasus.Satisfied with her work, Rainbow Dash begins a relaxing cloud-swim… only to be interrupted by the sounds of a distressed filly coming from a well below. Without hesitation, she dives into the well, easily rescuing the filly, and is met by a crowd of cheering ponies as she emerges. Blushing, she flies off, to the praise of Scootaloo, Snails and Snips.Later in the same day, a baby carriage goes careening off a steep road, heading straight for a cliff. Once again, Rainbow Dash is on hand to save the baby, and one again a cheering crowd meets her. This time, the praise goes to her head, and she poses and shows off to the crowd and cameras, to the bemusement of Applejack and Twilight. Yet another disaster strikes soon afterwards, wherein a group of elderly ponies find themselves on a collapsing balcony.
By this point, Rainbow Dash is actively egging on the crowds, while her friends lament her increasingly inflated ego. As she gives interviews and poses for the paparazzi in Sugarcube Corner, she even hires Spike to ghostwrite her autobiography. Twilight and Applejack are less than amused with her bragging and arrogance...Later, as she signs autographs for a line of waiting fillies, a plummeting Twinkling Balloon carrying a screaming mare gives Rainbow Dash another chance to perform a feat of heroism. Before she can get to the balloon, however, a mysterious pony in a mask and cape appears and saves the panicking pilot, leaving Rainbow to crash into the deflated balloon. The heroic pony vanishes as quickly as she came and the mayor declares her to be Mare Do Well, Ponyville's newest hero. The crowd cheers... except for Rainbow Dash, who bitterly snubs the new hero.Things quickly become worse for Rainbow Dash as Mare Do Well outperforms her in every regard. When a carriage filled with tourists goes flying down the steep road, Rainbow flubs the rescue whereas Mare Do Well effortlessly stops the carriage with her superior physical strength. A construction site devolves into pandemonium as a haywire crane and a collapsing structure put the workers in danger, and although Rainbow Dash manages to rescue one colt, Mare Do Well saves four in the same span of time, displaying an uncanny level of prediction. A leaky hydroelectric dam is easily plugged by Rainbow Dash, only to completely burst when she stops to compliment herself, leaving Mare Do Well to not only rescue Dash, but use unicorn magic to single-hoofedly repair the dam. Rainbow Dash's frustrations are only increased when, as she shows off her ability to fly, unlike Mare Do Well, the caped crusader herself flies by as well, now sporting pegasus wings.Back at Sugarcube Corner, Twilight, Fluttershy, Applejack and Rarity sing praises about Mare Do Well. An agitated Rainbow Dash refutes their claims, declaring herself to be a better hero than Mare Do Well, only to be called out on her jealousy by the others, including Spike. Unfortunately, there aren't any disasters that need heroism to be found, leaving Rainbow Dash to perform acts of heroism such as pushing Granny Smith across the street (she didn't want to cross), opening a jar of peanut butter (Amethyst Star easily opens it with her magic), and mowing the lawn.Dejected and alone, Rainbow Dash sulks on a raincloud, only to be interrupted by Scootaloo, who invites Rainbow Dash to Mare Do Well's thank-you parade. Quickly formulating an idea, Rainbow Dash follows her, and when Mare Do Well appears on stage, Rainbow confronts her and demands to remove her mask. A chase quickly begins throughout a secluded alley, and although Mare Do Well manages to lose her several times, Rainbow eventually corners and pounces on an unassuming Mare Do Well, and unmasks her to reveal… Pinkie Pie?Not only that, but two more Mare Do Wells appear and reveal themselves to be Twilight and Applejack, soon joined by Fluttershy and Rarity. The five reveal that they all had a hand in the plan; Applejack's strength saved the bus, Pinkie Pie used her Pinkie Sense to save the construction workers, Twilight magically repaired the dam, Fluttershy performed the fly-bys, and Rarity made the costumes. Rainbow questions why they would appear to force her out of the spotlight, and they reveal that although they enjoyed seeing Rainbow as a hero, her constant bragging and arrogance was uncalled for.Realizing her mistakes, Rainbow Dash begins to write a letter to the Princess, only to be cut off by Spike, who had already penned a letter in advance. When he insists on using his version, Rainbow Dash scares him off with a lighthearted prank, and begins writing her own version.
Always Someone Better: To Rainbow Dash's dismay, Mare Do Well outdoes her in many ways, such as being stronger than her, being able to see what's about to happen, and her powerful abilities in magic and being able to fly. Invoked by the others to try to humble Dash.
Also, when pressed for time, Rainbow Dash responds, "Yeah, yeah. I've got a good ten seconds to spare."
Pinkie Pie and Spike are easily scared, which is a nod to them being afraid of "zombie ponies" in "Bridle Gossip". Though Pinkie might just be pretending to be scared for fun, like she did for Nightmare Night.
Deadpan Snarker: Amethyst Star (the purple unicorn with the peanut butter), when asked to compliment Rainbow's "heroic" jar-opening skills, albeit interrupted.
Rainbow Dash: Would you say I was amazing? Amethyst Star: Aren't you milking this a bit? Rainbow Dash: Please, just answer the question. Was I or was I not amazing? Amethyst Star: Oh, you're amazing, alright. An amazingly— Rainbow Dash:Oh, look!! *goes off to save the grass*
Everypony Did It: A downplayed version. The masked hero turns out to be Twilight, Applejack, Pinkie Pie, and Fluttershy using their various talents to outdo Rainbow Dash, while Rarity provided the costumes.
Handbag of Hurt: Granny Smith's reaction to Rainbow Dash providing her with unsolicited help crossing a street.
The Mare Do Well is established as being stronger than Rainbow Dash, particularly in her hind legs. "Fall Weather Friends" established that Applejack's hind legs are stronger than Rainbow Dash's.
During the construction scene, Mare Do Well proves to be very agile, easily dodging every piece of falling debris. Rainbow Dash notes that she is fast, strong, and able to predict upcoming events - the last of which Pinkie Pie can do with her "Pinkie Sense."
While Twilight's magical aura color is seen in many episodes, one could point to "Boast Busters" as an episode that established her as one of the only unicorns capable of the large-scale magic necessary to move the rocks and repair the dam.
From the same scene, the Mare Do Well is seen with a unicorn horn, and then a moment later with pegasus wings as she buzzed past Rainbow Dash. Apart from Celestia, Luna, and Cadence (who are all ruled out for size considerations), no other winged unicorns were known to exist before Twilight became a Princess (at least in this generation, given the picture in "Hearts and Hooves Day") , indicating that more than one pony is posing as the Mare Do Well.
Flower Pot Drop: During The Reveal that Mare Do Well is some of the Mane 6 teaching Rainbow Dash a lesson, Pinkie Pie says she stopped the building collapse with her Pinkie Sense. She then detects a falling flowerpot with it, and dashes away to avoid it.
Foreshadowing: After the balloon rescue, Twilight seems awfully pleased to hear someone loudly praising Mare Do Well.
Hair Color Spoiler: A variant. The scene where the Mare Do Well uses magic to repair the dam probably gives away what's going on to older fans, though a later scene does restore some ambiguity (see Red Herring below).
Ineffectual Loner: Parodied. Rainbow Dash comes to realize she's upset that no one's paying attention to her and that she's lonely, but when Scootaloo tells her about Mare Do Well's thank-you parade, Dash says she wants to be alone.
Mundane Made Awesome: Opening a jar of peanut butter is very dangerous work! So is saving a lawn from weeds! Don't forget about escorting Granny Smith across the (not very) busy street (even though she didn't want to cross it)!
Mundane Utility: Unicorn magic… also useful for opening jars of peanut butter.
Nice Job Breaking It, Hero: If she had kept plugging the hole in the dam with her hoof instead of taking it out to pat herself on the back, Rainbow Dash would have been recognized as a hero again. In fact, Dash could have resolved most of the later situations had she been taking them seriously instead of bragging, wasting time, showing off and such. It is also implied that Rainbow made the crack in the dam worse by leaning on it.
In the larger scheme of things, the Mane cast (outside of Rainbow) initially cheer and support Rainbow's heroic efforts, and only after Rainbow lets this go to her head do they decide she's taking the hero thing too far.
No OSHA Compliance: A crane with a stuck lever goes haywire when a little force is applied to get it moving. A road inexplicably leads to the edge of a cliff (leading to two different disasters). A hydroelectric dam apparently has no one monitoring it for the obvious crack Rainbow spotted from the air.
Nothing Exciting Ever Happens Here: Granted, Ponyville has been host to some weird and catastrophic problems before, but it gets to almost Discordian levels of chaos all at once when the superheroing starts.
OOC Is Serious Business: Rainbow Dash realizes just how far from grace she has fallen after seeing that Scootaloo has switched her fan allegiance to Mare Do Well.
Rainbow Dash when you consider that she's been hailed as a hero not once, not twice, but three times before this, and not once was there indication that it went to her head.
Fluttershy not only joins in the Mare-do-Well ruse, but does a fly-by above the dam, just to show off. This was long before "Putting Your Hoof Down" gave her more confidence. Though it could be justified as she wasn't shy due to the fact she was disguised.
May further count as OOC Is Serious Business, considering how she already proved herself proved herself to be a fast flyer back in "Return Of Harmony: Part 2", even if she didn't even know her own speed.
Quote Mine: Spike when he's writing Rainbow Dash's "autobiography":
Applejack: And she's modest and humble. She lets her actions speak for themselves. Gotta admire that. Rainbow Dash: I don't have to admire that! I don't think she's all that great! Spike: She's... great. Rainbow Dash: I didn't say that.
Red Herring: Though the color of the magical aura that the Mare Do Well uses matches Twilight's, we see that Amethyst Star, whom Rainbow Dash helps with the jar of peanut butter, also has a magical aura that color. Coupled with her particular annoyance with Rainbow Dash, this may have been a deliberate Red Herring. It may have worked more effectively if it hadn't already been established that Mare Do Well could fly.
Also, it would have worked better had Twilight not stated that the dam-sealing spell was indicative of heavy studying. Who else but Twilight would have had the dedication?
After the construction site scene, Rainbow Dash comments that Mare Do Well "somehow knows what's gonna happen ahead of time". This might lead to suspicions that Mare Do Well was setting up these disasters. Turns out this was not the case; those accidents really were all coincidences.
Scooby-Dooby Doors: Rainbow's chase of Mare Do Well. Justified in that four ponies play her at different times.
Secret Identity Change Trick: If you pay attention, you'll notice that both Twilight and Applejack are in the crowd when Rainbow Dash confronts Mare Do Well on stage. This must mean that they took advantage of Rainbow Dash distracting everypony by chasing after Mare Do Well to sneak away and quickly change into their own Mare Do Well costumes.
Same with Fluttershy: one of the Mare Do Well's in the chase scene is clearly a Pegasus, but when we see Fluttershy next, she's out of the outfit.
Talking Is a Free Action: Averted. The reason Rainbow Dash can't save the construction workers is because she insists on shouting "Never fear, Rainbow Dash is here!" and keeps getting interrupted by falling pieces of rubble and bricks.
Title Drop: Done by the mayor after the introduction of the mystery hero.
Took a Level in Badass: Pinkie Pie, who up to this point had been portrayed as one of the less physical ponies (unless she's angry), uses speed, agility, and her Pinkie Sense to good measure in saving the construction workers.
Visual Pun: The hydroelectric dam is modeled after WHICH real-life facility?
Well Intentioned Replacement: The mane 5 and their posing of the Mare Do Well to "replace" Rainbow Dash as the town's hero all just part of their plan to try to humble her.
What Happened to the Mouse?: Though the mane cast explains which role they played during the whole episode, it is never explained which of the mane cast as Mare Do Well saved Cherry Berry from her falling air balloon. Judging by the superb jumping skill, which would require powerful legs, it was most likely Applejack, although Pinkie Pie probably could do the same, so it's a toss up.
Also, we never find out what happens to the parade after it's left behind or if anypony other than Rainbow Dash ever learned about Mare Do Well's true identity.
Winged Unicorn: Mare Do Well appears to be this after fixing the dam. It's just Twilight and Fluttershy switching places. Thanks to the hat and cape, no one can tell that Mare Do Well doesn't always have a uni-horn or pegasus wings all the time.
Your Other Left: Said by the construction worker Rainbow Dash is carrying while rubble falls around them. Interestingly, he's facing the same way as her.