(spoilers)
Right away, we see Juniper Montage is still furious at the main 7 for stopping her greedy attempts in last week's special. While she's on break from her new job at the theater's concession stand, she finds a hand mirror that has just been enhanced by a stray burst of Equestrian magic (so I guess this is how new magical anomalies are going to occur in this series from now on, stray bursts of magic leaking from the portal, as seen at the very end of Legend of Everfree).
Meanwhile, Sunset is not only needlessly concerned about the recent lack of magical incidents, but has also just run out of pages in her magical journal, so Princess Twilight asks her to come back to Equestria to get a replacement journal. However, when she gets there, Twilight and the others are away on friendship business, so Starlight Glimmer (whom Sunset and her friends are already aware of thanks to Princess Twilight's messages) is the only one around to give her the new journal. But once Sunset has the new journal and prepares to return to the human world, Starlight asks if she could go there as well, and Sunset eventually decides to let her come.
While that's going on, Juniper is discovering the powers of her new magic mirror, such as showing her what she wants to see herself as (a famous and highly adored movie star), and the ability to make things disappear into the mirror by simply wishing it away, including all six of Sunset's friends. When Sunset encounters her (and uses her magic to get answers from Juniper's memories), Juniper (who is clearly growing more crazy from the magic mirror) does not hesitate to trap her as well. Now Starlight Glimmer is the only one around to do anything about the situation. Even worse, since all of the main 7 are now wearing their magical geodes, it causes a reaction that turns Juniper in a freakishly tall, super strong (and kinda ugly) woman who is delusionally convinced that she is exactly the famous movie star she always wanted to be (even though we clearly see all bystanders running away in fear).
Starlight knows that the first thing she needs to do is get the mirror out of Juniper's hand. While she is able to grab that mirror and keep it away, the ensuing chase includes incidents that cause the mirror to start fracturing, leaving the main 7 inside with progressively less space to stand on. Finally, Starlight convinces Juniper that if she really wanted to be liked by everyone, she should consider friendship, regardless of her past actions. Juniper is hesitant, but agrees to wish the girls out of the mirror, and everything is restored to normal (just as the mirror has been reduced to just a single small fragment).
Juniper doubts she'll be forgiven, but the girls say otherwise, citing the past experiences of Starlight, human Twilight, and Sunset. (And Pinkie's remark after that was right, they sure are quite a forgiving group.) Finally, after everything, Sunset gets a message from Princess Twilight saying that she's willing to let Starlight stay in the human world for a few days, so it's possible we may see her again in future installments in the Equestria Girls series.
It sure was really nice to see Starlight Glimmer from Equestria getting to be part of the Equestria Girls series, and we even got a brief return of pony Sunset Shimmer (though her unicorn magic now seems to have a different color compared to what we saw in the first movie). Those are pretty much the only reasons why this one was my favorite of the three specials.
(end spoilers)
And that's it for this years edition of Equestria Girls. Now we just have to wait for news on when season 7 of the main show will resume.
