Dwindling Party: The mane cast gets gradually smaller as the shorts progress. By "PARTY.MOV", Twilight is the only Element bearer still able to do anything. This is undone due to Applejack causing a Cosmic Retcon.
Jerkass: All of them, but especially Rarity. Ironically, Fluttershy still seems to be the nicest of the group, even when she turns out to be an Axe Crazy psychopath!
Heel-Face Turn: The ending of SWAG.MOV seems to point to at least most of them becoming better ponies, although Paco's Twitter states that Rarity is still abusing him.
Kick the Dog: In "SWAG.MOV", when Applejack returns to Ponyville after her adventures in Equestria Prime and tries to tell her friends about how she saved the multiverse, they tell her nobody cares. Considering how Twilus told her what she's done was the most important thing anyone in existence has ever done, and that her own universe would have been forever destroyed by Rainbow Dash's Sonic Rainboom if not for the Cosmic Retcon her absence caused, this is a hard blow.
Those Wacky Nazis: Her real last name is "Mengele", and she calls Rainbow Dash's defeat of Discord "wunderbar".
Writer's Block: Twilight struggles to write a letter to Princess Celestia because she hasn't learned anything, so she screws it up and throws it in the trash, which is full of other balls of screwed up paper. Not that Princess Celestia is even alive at that point...
Wrong Genre Savvy: Twilight's theories about resurrecting dead bodies are all from movies, and she doesn't understand why they don't work. It's because the body she tries resurrecting (i.e., Rainbow Dash) isn't dead.
Spike T. Dragonowitz
"Am I the only sane one in this crazy world of technicolor pony weirdos?!"
Twilight's baby dragon assistant, who'd much rather crack jokes—and do crack—than be of any actual assistance. Ironically enough, his pothead tendencies may make him the most rational living being in Equestria, period. Voiced by Max Gilardi.
Catch Phrase: Whenever someone is injured or dead, Spike hovers over them and says, "Yo, [character name]... Y'alright?"
Determinator: Summed up nicely by Twilight Prime at the end of Ask Jappleack:
Twilight Prime: She proved that whether you adhere to the laws of faith or of facts, it always boils down to the truth that no hurdle is too high for the sheer force of an indomitable spirit. She proved once and for all...that nopony can tell her what to do.
Earn Your Happy Ending: Even if the others don't appreciate it, she still becomes a better pony and saves the multiverse from Appelox. In the end, she gets her sister back (and likely Winona too) and she and her friends are on good terms again. She probably worked the hardest for all this.
Heroic BSOD: Jappleack goes through this after Apple Bloom dies.
Hero of Another Story: She misses most of the main storyline due to having her own adventure in Equestria Prime, and only returns after Discord's been defeated. However, because her actions instigate a Cosmic Retcon that allows Discord to be defeated, she's not entirely inconsequential.
Jerk with a Heart of Gold: Despite her abuse, she's shown to genuinely love Apple Bloom and is heartbroken when she dies. Post-Character Development, she still insults her sister after she comes back to life, but now it's more playful than cruel.
Stranger in a Familiar Land: At the end of her journey, Applejack becomes the only pony in her world to understand love and friendship, and dedicates the rest of her life to teaching what she's learned to her friends. She's already had some success with Apple Bloom.
Took a Level in Kindness: She starts out as a hateful Jerkass who abuses her little sister, and answers many of the questions on her Tumblr like any troll would. Once her sister dies and she discovers the values of love and tolerance from Applejack Prime, she becomes much more mature, loving, and considerate.
I0itsmonica: What happened to you, Jappleack? Jappleack: Meh, I dunno. I guess I just sort of...grew up.
Yank the Dog's Chain: Not long after she realizes how much Apple Bloom means to her, Apple Bloom dies.
Just as she discovers happiness in Equestria Prime, Appelox comes along and tries to destroy it. When she kills Appelox, she finds that her continued presence in Equestria Prime will tear all of reality asunder, forcing her to leave her new friends.
"Yeah, why don'tcha suck my tit, you dumb bitch? Hehehehe! Swag."
An ass of a pony who gets a kick out of kicking others around. And swag. Voiced by Max Gilardi.
Back from the Dead: Subverted and averted; Twilight attempts to do resurrect her in "MAGIC.MOV", but to no effect. She only comes back in "SWAG.MOV", two episodes later, to which she reveals she was in a coma.
Cool Sword: Gets to wield the Sword of the Holy Titans, a gigantic magical sword that was one of the only things Twilight Prime even considered could work on Appelox, in the Grand Finale and uses it to behead Discord.
Jerk with a Heart of Gold: This is especially true when she ends up being the one to protect Ponyville and stop Discord. The ending implies she may have learned from her mistakes since she seems much nicer to her friends at that point.
Took a Level in Kindness: At the end of "SWAG.MOV", she risks her life (and loses her wings) to save Ponyville from Discord and is actually the one who initiates a Group Hug when she realizes the group is finally together again. Considering it seems Fluttershy never snapped in that timeline (judging by the lack of mutilated animals in her shed), she may have eased up on her as well.
Pinkamena Diane "Pinkie" Pie
"My daddy makes me put glass in my vagina."
A pink party pony who gets a bit too off on parties. Best friends with Rainbow Dash. Voiced by Arin Hanson in her first appearance, and by Max Gilardi in all other appearances.
Mad Artist: Her shed's filled with the mutilated corpses of dead animals that are hung up on the walls.
Pinkie: Wow, Fluttershy sure has a lot of weird art...
Seems subverted after Rainbow Dash reset time where it's completely absent when we see the interior, probably due to events (and Rainbow Dash) changing for the better. In fact, her shed appears to be just a private relaxation place.
Implied this may happen to Discord (well, his severed head, anyway) at the end of "SWAG.MOV" when his head lands right next to her shed, although her shed was already reformed and she only mildly annoyed says to him, "you're in my shed".
Shout-Out: Her voice is modeled after Fat Albert. Taken up a notch when she sings a variation of the theme song.
Pet the Dog: Is shown to be comforting Sweetie Belle when she is scared in "SWAG.MOV". She may be an evil sweatshop owner and force several dozen Mexicans into slavery, but hey, she at least cares about her sister.
Put on a Bus: All but disappears from the story at the end of "DRESS.MOV" after her sweatshop workers stage a revolution.
Visual Pun: Selfish, greedy Rarity constantly talks about how generous she is. There are only two generous things about her in this show: her obese figure, and the beating she gets when her Mexican workers start a "revolución".
Applejack's little sister who just can't wait for the happiest day of her life: the day she gets her cutie mark! Also appears in Ask Jappleack, which shows her less-than-healthy relationship with her sister. Voiced by Esther Nho.
Back from the Dead: A Cosmic Retcon triggered when Jappleack kills Appelox makes it so Apple Bloom never died due to Rainbow Dash distracting Discord for a few moments, allowing her to escape.
Throw the Dog a Bone: Thanks to the Cosmic Retcon caused by her sister, history is changed so that not only does she survive, she also gets to keep her cutie mark. On top of that, Jappleack returns from the canon universe a much nicer pony and has realized how much Apple Bloom means to her.
Click here to see "Derpy post toasterization"
A lovable, wall-eyed pony who gets brutally murdered by Fluttershy and turned into a decorative toaster cozy.
Butt Monkey: In addition to what already happened to her, she's the only named character who's death isn't undone by the Cosmic Retcon. She may never have been dead at all if her scene in "SWAG.MOV" is anything to go by.
Companion Cube: She's one of Paco's best friends despite being a toaster cozy.
The ruler of Equestria, who decides to take matters into her own hooves when Discord comes rampaging.
Back from the Dead: Implied; the same Cosmic Retcon triggered by Applejack that prevents Apple Bloom's death also naturally prevents her own, since she dies after Apple Bloom and Discord's killed before she can try to fight him.
Hostile-ish Blog Takeover: Briefly takes over Jappleack's Tumblr after she knocks Jappleack out cold in preemptive self-defense, but only until she is able to get Twilight Prime to come over and explain what's going on.
"Take a deep breath friend, we're going down the rabbit hole."
— "Ask Jappleack"
Twilight's Equestria Prime counterpart. She surveys the goings on of countless alternate universes, including her own, and is Jappleack's go-to pony for info on the maddening events that sent her to her world.
Agree to Disagree: She and Applejack Prime frequently argue due to their opposing beliefs on the history of Equestria. Despite their arguments, the two remain good friends.
Guardian of the Multiverse: Twilight Prime falls under this with her Transuniversal View-O-Scope that allows her to observe the entire pony Tumblrverse.
Science Hero: Twilight Prime is more liable to rely on science rather than magic to solve a problem.
Straw Atheist: She refuses to believe Equestria was made by the Holy Titans of Harmony, which puts her at odds with Applejack Prime. When Appelox (one of the Titans) attacks Equestria, she's forced to change her attitude fast in order to make a decent plan.
"Do you honestly think you can fare better against me than my brothers and sisters did?"
— "Ask Jappleack"
The Holy Titan of Honesty who can be found in the void between the worlds. Consumed by gluttony, he had devoured his fellow Titan siblings and now feasts on the essence of the entire multiverse.
Last of His Kind: Believed to be the case, but after Jappleack bites his head off to save Equestria Prime, Twilus, the Holy Titan of Magic, is freed from inside him and states her other siblings will reform now that Appelox is dead.