Sunset being a gamer makes some sense if you remember a study that showed playing video games helped with hand-eye coordination. Having been a pony for most of her life, Sunset would need all the hand practice she can get.
A bit of possible fridge tearjerker concerning Flash being a part of the Chemistry club. He most likely joined the club as a way to get closer to Human Twilight only to later find out that it wouldnt work. Although, on a brighter note, the fact that hes still in a club with Human Twilight could possibly mean he's somewhat moved on or at least now has a stable friendship with this Twilight.
Sunset is usually the most mature, yet she has no trouble believing a sea monster could roam in "Unsolved Selfie Mysteries", while Twilight is skeptical. Of course, Sunset is from Equestria, where sea monsters are a much more realistic possibility.
The background students at CHS now include a few faces that were Crystal Prep Shadowbolts earlier. In retrospect, Principal Cinch's fall from grace isn't so surprising since, in addition to tying at the Friendship Games and endangering students, there has been a few defection among the Crystal Prep ranks (in addition to her best student, Twilight Sparkle). That sure couldn't have helped her "reputation" before the school board. Her replacement by Dean Cadance was bound to happen.
Timber hiding behind Twilight in Unsolved Selfie Mysteries can make a bit of sense considering his girlfriend is capable of transforming into a Magical Girl and can fight back against monsters. Timber, however, is a normal human whose first experience trying to fight back against a magical monster was a total failure as he couldnt even slow them down.
It's actually possible (and plausible) that Rarity's one-person-and-one-pig club was founded for the sole purpose of teaching Applejack and Rainbow Dash a lesson about getting too competitive.
Of course Applejack would want Sunset Shimmer to wear the pony costume with her! Sunset is a pony from Equestria after all.
And why Sunset declined the offer? Her reaction to the costume at the party makes it clear: She was jarred by it.
Fluttershy was the only one playing video games, even through Sunset is an avid gamer. However, this makes sense when you notice that the video game Fluttershy is playing is the same one she and Sunset played in "Game Stream", and the troubles Sunset went while trying to play.
Why would Sunset have horse shoes if they are of no use for her in the human world? Well, as a pony, they probably serve as a way to remember her home.
Sunset (and very likely her friends) may not be fans of Tirek's Revenge if they ever found out that Tirek is real, went on a rampage through Equestria before being defeated, and is currently in Tartarus, awaiting his chance to escape again.
Especially considering that it was Celestia who helped prolong Tirek's revenge by sending in Discord alone and insisting Twilight doesn't rely on her friends.
As if magic turning a poor individual into an insane monster wasn't bad enough, "My Little Shop of Horrors" shows it's also possible to unknowingly obtain an enchanted object that could cause a lot of trouble if used.
Pinkie Pie's magic got strong enough to affect the sugar inside an apple, so what would happen if Pinkie tried tossing a person? Like a child or a cheerleader? Would her magic have affected the sugar in their bodies and make it explode?
Presumably when working on her magic, she will eventually learn how to also de-charge things. So if she accidentally charges a person with her magic, she could hopefully remove the energy before something bad happens.
Furthermore, said apple explosion happened during a surge in magical powers, so Pinkie might not be able to replicate such behavior during normal operation.
Alternative Title(s):My Little Pony Equestria Girls Costume Conundrum