1.The story was copy-pasted from the premiere, but with a different villain and setting, kinda like how some people complete some assignements by copying Wikipedia and changing a few words to make it
look like
they thought of it without any help. THAT MAKES IT NEITHER ORIGINAL NOR INTERESTING!!
2.The movie had a
completely unneccesary B-plot with Flash Sentry and Twilight, which
had to be some kind of weird, messed up, censor-dodging zoophilia (because Twily was in human form). If Flash had an important role in the movie, it would've made more sense, but he's
literally nothing more than a fifth wheel. Sure, he matters to the story, but
only because Sunset used him to gain popularity
long before the events of the movie. FLASH SENTRY HAD LITERALLY NO USE IN THAT MOVIE EXCEPT MAKING ME CRINGE WHEN HE'S NEAR TWILIGHT!!!
3.Sunset's plan is incredibly stupid. What was it again? Oh yeah! Transform a bunch of
teenagers into demons and take over Equestria. Honestly, Twilight didn't even
need to go through that mirror to get that crown back, because the Mane 6 have faced much,
much worse that that (Changelings, anyone?), not to mention that they also have Discord on their side! (To be fair though, Sunset didn't know about the latter.) In other words, Sunset goofed.
4.How the **** did Twilight not know about Sunset Shimmer? One of the comics literally shows that Sunset went thought the Crystal Mirror when Twilight was a filly. Knowing Celestia, I understand how Twilight might not know what she did, but come on! Twilight didn't even
knew who she was (but Sunset did, further proving what the comic shows). That is just so dumb!
5.The writers just
had to make a portal to another world that opens
at the same time that Twilight is inside the Crystal Castle.
How convenient! Speaking of, said portal was in Canterlot Castle before and the Crystal Empire was missing for about 1000 years before S3. How did Sunset managed to know where to go to find the Element of Magic? Sure, some events could be unseen, such as her finding her way, but considering how huge the castle is, she must've been in Equestria for hours before finding the room and/or found it by pure coincidence. If it's the first one, Crystal Guards are clearly underqualified for their job.
6.How did Twilight managed to be inside of CHS? If she's undercover as a student, she'd basically need to pay for her admission and/or school supplies, but she has no human money. Sunset being a power-hungry bully, we can assume she stole her way to those, but Twilight? Then again, they
could be free, but why would it? And if she's
not a student, she'd likely get kicked out, mainly because the human Twilight is from CHS's biggest rival, Crystal Prep.
7.It was never explained why the Rainbooms could transform into half-ponies in this movie and the explaination from its sequel is terrible, but at least, said explanation is just a theory and not an actual fact. Plus, Rarity and Twilight can't use magic (besides the Magic of Friendship), which is dumb because it downgrades unicorns.
8.
Everything in Canterlot High School is taken off from clichés that are used by countless shows, such as the high school setting itself, which has basically been used more often than Mario in a Nintendo game.