Spike is leading the love of his life, Rarity, through a wonderful world made of ice cream... until he hears the clopping of hooves, whereupon he wakes up to find Twilight nervously pacing at 3:00 am. Turns out she's discomforted because, after planning her schedule for the month, she didn't allocate any time to work on next month's schedule, so now her whole year could be thrown off. Annoyed, Spike returns to bed in hopes of returning to ice cream land.Later that morning, Twilight is still fixing her various schedules when a burst of purple magic abruptly goes off in the middle of the room. It subsides to reveal a purple unicorn with a torn spy suit, an eye patch, a disheveled mane, a bandaged head, and a scar on her face — Twilight herself! Now there are two Twilights, except one's from the future, and looks like she just walked off the set of Escape from New York. Is she perhaps from some distant time, when Equestria is embroiled in some sort of epic pony war?
Future Twilight: Actually, I'm from next Tuesday morning.
Future!Twilight has an important message to convey, but Present!Twilight is so excited at the prospect of Time Travel that she's full of questions. Future!Twilight has to put a hoof to her mouth to get her past self to shut up, but before she can deliver her message, she disappears in a flash of light. Suddenly realizing that she should have listened to herself, Twilight is charged up to prevent whatever unspecified cataclysm that's about to befall Equestria!Rushing outside, Twilight warns Ponyville of the impending calamity; everypony laughs at firstnote including a certain brown pony with an hourglass cutie mark, but she soon convinces them to take her warning seriously. The pegasi search the skies across Equestria, while everypony else fixes every crack, loose bolt, and stray hair across Ponyville. But even taking every preventive measure doesn't seem enough...Suddenly, Cerberus, Guardian of the Gates of Tartarus — where all the evil beings of Equestria are kept — appears in the middle of Ponyville! He must be the disaster! Steeling herself, Twilight prepares for battle... until Fluttershy tames the beast by tickling his tummy. Realizing that Tartarus is still unprotected, Twilight borrows a ball from Pinkie Pienote she keeps them hidden around Ponyville just in case, then lures the big lug home.Twilight Sparkle returns home the next morning, whereupon Spike burps up a "lost dog" flyer from Princess Celestia, which gives her a paper cut on her cheek — the exact same one her future self had! Since this means the future hasn't changed and the great disaster is still to come, Twilight decides to do nothing at all until Tuesday, not even move. Spike and Rainbow Dash decide to have fun at her expense, with Spike eating ice cream by the tubful and tickling her. Twilight telekinetically tosses Spike away, causing him to accidentally belch fire and scorch Twilight's mane, giving her the same style her future self had! Pony Armageddon is still underway!Spike suggests a visit to a fortune teller, "Madame Pinkie". With her gypsy magic, Pinkie Pie tells Twilight that… she will get a really awesome birthday present next year. Twilight asks her to use her Pinkie Sense instead, but Pinkie explains that it's only for vague, immediate events — like a flower pot suddenly falling out of the sky onto Twilight's head.Pinkie Pie visits Twilight the next day, who has an epiphany (as well as a bandage) — disaster can be averted if she monitors everything until Tuesday! But when Pinkie reminds her that Tuesday is actually tomorrow, Twilight gets into a panic, then ends up looking at the sun through a telescope and blinds herself. While Pinkie provides an emergency eye patch from her secret stashes around townnote you know, just in case, Twilight decides there's only one thing left to do: Stop time itself.Remembering that Future!Twilight said that the time spells were locked away in the Star Swirl the Bearded Wing of the Canterlot Archives, Twilight takes Spike and Pinkie with her to Canterlot. After donning black catsuits, eating ice cream, sneaking past guards, going in a circle, eating more ice cream, and having a helpful guard let them into the wing, the trio begin a frantic search for the time spells — but they're too late! Dawn is breaking, Tuesday morning is here! As Twilight realizes she now looks exactly like her future self, she panics, bracing for the impending disaster......and nothing happens. Princess Celestia walks by and says hello. The sun is shining. It's a pretty nice day.Twilight finally realizes that she's been worrying too much, and pledges to solve problems as they come and let the future handle itself. As Twilight muses that it would have been better if only she had learned this sooner, Pinkie Pie shows a scroll that she found, which can send someone back in time for a few minutes. Twilight decides to use that to warn her past self not to worry about the future....oh, so that's where Future Twilight came from! Oh well, it's Past!Twilight's problem now. After a few laughs, the girls head home, especially now that Spike has a stomachache from eating too much ice cream. He had assumed that would be Future!Spike's problem... until he became Future!Spike.
Tropes present in this episode (YMMV tropes can be found here):
Aesop Amnesia: In just the previous episode, Fluttershy learns to stop being so submissive and stand up for herself, make her voice heard. In this episode, she's seen struggling under the weight of dozens of Pinkie Pie's bags while Pinkie Pie has fun with some balloons. We would need to see the scene in which she and Pinkie Pie decide who carries what to decide for sure.
An Aesop: An interesting two-fer. Twilight learns not to worry so much about what might happen tomorrow— while Spike (by way of an ice cream stomachache) learns not to just shrug off consequences to the future.
The Alcatraz: Implied with the Gates of Tartarus, as it houses all manner of Equestrian monsters.
All for Nothing: Played straight, except for the fact that Ponyville's infrastructure got a nice sprucing up with all the preventative maintenance.
Amusing Injuries: Twilight is the recipient of all of them this episode, slowly turning her into Future Twilight until she catches up with herself. Both Future and Past Twilight play up the injuries for all they're worth, even mistaking a paper cut for a scar.
Star Swirl the Bearded is mentioned once again, and the Star Swirl "wing" in the Canterlot Library that was mentioned is basically just an extra-secured room — which is as big as the entire Ponyville library. A section of the library named after him was alluded to from the start.
Cock-a-Doodle Dawn: We don't see the bird, but we do hear it in the distance when the sun comes up on Tuesday.
Comically Missing the Point: Pinkie doesn't understand why Twilight has to sneak into the Canterlot Archives (because she thinks Twilight wants to find out about the present she's going to get).
Pinkie manages to fit her unruly mane into a tight-fitting costume again.
In the same vein, Spike's able to get his spikes to lay flat within the costume.
Compressed Vice: Spike seems awfully fixated on ice cream this week. Unlike candy in "Luna Eclipsed", there's no real motivation here. He just does it because the effects will be someone else's problem — specifically, Future Spike's.
Dude, Where's My Respect?: Averted for once. Twilight doesn't make the best start to explaining to the town that she just got a warning about some unknown disaster from her future self (because of what she was wearing at that time), but once it's clear that she's serious, she's afforded all the respect a pony who saved the world twice deserves. Also, when in Canterlot Castle, a guard recognizes Twilight and lets her into the restricted archive wing she was trying to get into without any grief.
Eye Scream: That eye patch on Future Twilight? She trusted Pinkie to calibrate her telescope so it would be safe to look at the sun. You can connect the dots from there. Though Pinkie did explain that she had no idea whether she did what Twilight asked.
Face Hoof: Twilight, upon finally realizing that her time-traveling is what caused her ordeal.
Failed a Spot Check: Twilight doesn't notice that the Star Swirl the Bearded Wing is right across the hall from where they came in.
Twilight: I don't understand; it's supposed to be right here. How are we supposed to find it now? Pinkie Pie: Maybe we should ask somepony in the Star Swirl the Bearded Wing. [beat] Twilight:Huh, how did I miss that?
Fangirl: Twilight, of herself, and why Future!Twilight can't get a word in edgewise.
Flower Pot Drop: When Twilight asks the gypsy Pinkie Pie if she can use her Pinkie Sense to detect what will happen in the future, Pinkie explains that it's only for immediate emergencies. Cue "twitchy tail" and flowerpot to Twilight's head.
Future Badass: Parodied. Future Twilight comes from only a few days in the future, and she only looks the way she does because of a series of random accidents.
Future Me Scares Me / I Hate Past Me: Future Twilight's appearance scares Twilight a bit before she becomes thrilled with the whole Time Travel thing. Future Twilight, in turn, is frustrated by her past self's refusal to calm down and listen to what she has to say.
The Guards Must Be Crazy: Comically subverted. After Twilight tries hard to sneak into a locked library section containing powerful magical artifacts, a guard she bumps into just lets her in... because as Princess Celestia's protégé, she's allowed in there, which Twilight herself forgets.
When Spike addresses that Twilight's pacing has worn a groove into the floor.
Twilight: I don't have time for another one of your lectures, Spike! This is serious! Spike:My lectures?
Meta example: One of the ponies who laugh at Twilight's claim of being warned by her future self is Doctor Whooves.
Insane Troll Logic: Twilight first assumes that Future Twilight's warning is dire simply because of her appearance, and then goes through four phases to avert the future: Do something to try to stop it, do nothing to cause it happen, use magic to try to figure out what happens, and use science to try to figure out what happens. Finally, she decides the only way to stop the disaster is to stop time itself so Tuesday morning never comes.
It Is Pronounced Tro PAY: Twilight pronounces Tartarus as the Greek "Tar-Tar-Os", and not "Tar-tur-us" like is most common in English.
Mind Screw: Just a little bit, which is for the best since we have the target demographic's sanity to watch out for. At the end of the episode, Twilight just wanted to warn her past self about not worrying the future, a lesson she would have not learned if her future self didn't make her paranoid. Even worse is how Twilight got the knowledge of where the scrolls are: Future Twilight got it from Past, who got it from Future, who got it from Past, who got it from Future, who got it from Past...
Mundane Fantastic: In Princess Celestia's mail to Twilight, she refers to Cerberus having left the gates of Tartarus as a "lost dog" matter.
Twilight's incessant questions about time travel cause her not to hear what her future self wants to warn her about. On the other hoof, if Twilight hadn't gone back in time in the first place, none of this would have happened.
At the same time, averted: The town has had a thorough maintenance period to be ready for the next major disaster, and Cerberus, the Guardian of the Gates to Tartarus, is back where he belongs. All are unrelated to Twilight's original goal, but they have beneficial side effects.
Nopony Here But Us Statues: Twilight, Pinkie and Spike pose as statues in order to hide from the guards, even though they didn't really need to.
Noodle Incident: Twilight considers trimming Pinkie's mane to be an important part of disaster-proofing the town. Knowing Pinkie, there's quite a story behind that.
Offscreen Moment of Awesome: Twilight's journey to return Cerberus to the Gates of Tartarus is never shown, but considering how disheveled she is upon her return, it wasn't easy.
Ooh, Me Accent's Slipping: Twilight's voice is a bit off in a few scenes, sounding more like Tara Strong's natural voice. Rainbow Dash's is unusually deep in the scene where Twilight is trying not to move.
Paranoia Gambit: Future Twilight accidentally doing this is what kickstarts the episode's plot.
Parental Bonus: While a certain other wizard has helped the target demographic know about Cerberus, the mythological concept of Tartarus holding back ancient evils is likely a tad above them.
Reality Ensues: Twilight forgets a basic fact about herself when she breaks into the Archives: she is the personal protege of Princess Celestia herself, who else outside maybe senior government ministers would have more privileged access than her?
Schedule Fanatic: While Twilight is known for this sort of thing, this episode kicks it up a notch when, at the start the episode, she's seen obsessing over the fact that, in this month's schedule, she didn't make time to make next month's schedule.
Sealed Evil in a Can: The episode reveals that there're a bunch of these things sealed away in Tartarus that are guarded by Cerberus.
Self-Fulfilling Prophecy: All of Twilight's worrying results in her acquiring all the ominous physical differences that Future!Twilight had.
Shaggy Dog Story: The episode is a week's worth of worry, strife and grief, which all led up to the dramatic reveal of a very pretty sunrise. It was all caused by Twilight using magic to warn herself (unsuccessfully) to not commit a bunch of worry, strife and grief over the next week.
The music playing during Twilight's encounter with herself is a rendition of the Doctor Who theme "I am the Doctor". Also, before Future!Twilight materializes, the iconic "house key scraping piano string" sound of the TARDIS can be heard.
This episode shares some similarities with the Duckman episode "The Once and Future Duck". In both episodes, the main characters get warnings from future selves, try to avert disaster by not moving, and learn in the end not to stress out about the future.
Super OCD: Twilight obsessing about not scheduling time to schedule her next schedule. She's also so caught up in tracking down the Star Swirl Wing by her calculations that she fails to notice it right at the point they started.
Temporal Paradox: Of the "Information Loop" variety: Future Twilight tells her past self where she found the spell to travel in time, which is why Twilight knows where to look for time manipulation spells when she needs one, which is why she ends up sending herself to the past and telling her past self where she found the spell to travel in time, which is why Past Twilight knows where to look for time manipulation spells, oh, no, I've gone cross-eyed...
Tickle Torture: Spike does this briefly to Twilight when she attempts to avert disaster by not moving at all.
Time Travel: The plot kicks off because Twilight travels back in time to tell herself something.
Time Travel Tense Trouble: Some of the dialog raises this issue, and Spike's ice cream tummyache is a direct play on that, assuming that it would have been Future Spike's problem.
Present Twilight: What a mess she is! Or I am. Or... will be!
To Hell and Back: Lampshaded. After disaster-proofing Equestria, Twilight comments that "Future Twilight looked like she'd been through a horrible ordeal." Moments later, she's off on an "epic adventure" to return Cerberus to the gates of Tartarus.
Unusually Uninteresting Sight: Twilight assumes the Canterlot Archives will be heavily guarded and thus she'll need to sneak in, hence the Spy Catsuit. She seems to have completely forgotten that it isn't out of place for Celestia's personal student to be seen there.
Additionally, the guard pony, and Celestia, don't bat an eye at seeing a disheveled Twilight in torn catsuit acting like she is in a spy movie. Celestia even compliments her "new" hairstyle.
Urine Trouble: Narrowly averted when Twilight calls Cerberus away from doing his business on the ice cream store.
What Happened to the Mouse?: Twilight's scheduling conflict is never brought up after she receives the visit from her future self. Likely made worse since "deal with warning from the future" was not on her original schedule.
You Can Panic Now: Pinkie Pie tries to encourage everypony to panic when Cerberus approaches.
She also ask if anyone wants to panic with her when Twilight is telling everyone about the warning from Future Twilight.
You Can't Fight Fate: Twilight attempts to change the future in order to prevent a perceived catastrophe, only as the days progress, signs keep appearing in the form of injuries, leading Twilight to believe the catastrophe is still on its way.