Demon Shimmer
After Twilight was declared Princess of the Fall Formal, Sunset Shimmer took things to extreme measures by putting on her crown, but she transformed into a raging she-demon and was overwhelmed by equestrian magic. She may have gained control of every student of CHS, but Twilight and the rest of the Mane 6 not only turned Sunset and the students back to normal, but showed her the magic of friendship.
The Dazzlings (The Sirens)
Adagio Dazzle, Aria Blaze, and Sonata Dusk used the negative energy to summon their monstrous sea creatures known as the sirens at the music festival. They have powerful soundwaves that easily overpowered the Rainbooms. But the reformed Sunset Shimmer got the band back together and unleashed their powerful magic against the dazzlings, and broke their spell.
Midnight Sparkle
Like Sunset Shimmer, Sci Twi transformed into a demon, and was overwhelmed by equestrian magic after Principal Cinch and the students of Crystal Prep made her release all the magic that she stole from Sunset's friends. She created dimensional rifts, and said that she wants to understand magic. But Sunset Shimmer used Sci Twi's device to transform into Daydream Shimmer, and showed her the magic of friendship. Sci Twi was turned back to normal and CHS was saved by Sunset Shimmer.
Gaia Everfree
Sunset Shimmer and Twilight founded out that Gloriosa Daisy was using magic with the geodes, because she was trying to save the camp from Filthy Rich closing it down. After she got the rest of them, she transformed into Gaia Everfree. She went to the camp, and created a wall of thorns around it. The Mane 5 hold her off until Twilight and Sunset arrived. Timber tried to stop her, but she wouldn't listen. Gloriosa created a dome of brambles, causing a chain reaction where all the thorns began to grow uncontrollably. Twilight Sparkle embraced the magic of friendship and got the geodes for Sunset and her friends. The Humane 7 used their power to save Camp Everfree, and turned Gloriosa Daisy back to normal.
Juniper Monstar
Juniper Montage trapped the Humane 7 inside the mirror, causing a chain reaction with their geodes and transformed her into Juniper Monstar. Her magical ability is creating a hallucination where people adore her, but on the inside, they fear her. Starlight Glimmer reasoned with her that friendship is more important than fame. Juniper made her final wish and set the girls free from the mirror before it shattered completely. Juniper was reformed at the end of Mirror Magic thanks to the Humane 7 and Starlight.
Wallflower Blush
Wallflower may be shy, but she found something in the forest behind the Canterlot High School. It was the memory stone. She took the memories from Sunset Shimmer's friends at first. At the very end, she took Sunset's memories, and that is where the Humane 6 saw the real truth. The Humane 7 ponied up and destroyed the stone and got their memories back just in time before the sun went down. Wallflower was easily reformed by Sunset Shimmer and her friends.
Vignette Valencia
Vignette Valencia is the boss of the theme park, but when it comes to fashion and design, she always finds a way to make them perfect. Equestria magic got into her smartphone, which allows her to transport an object or person to another area and make fake copies. The first victim was Fluttershy, then Rainbow Dash, then Sci Twi, Pinkie and Sunset. The reason why Vignette didn't got Rarity because the geode of generosity acted as a defense mechanism. Rarijack thought their friends were trapped inside the phone, but it turned out that Vignette's phone was a teleporter and they were in the vacant white room in the park and that was the biggest twist. Rarity and the Rainbooms ponied up once more and destroyed the magical phone. Vignette was reformed at the end and the Rainbooms sung their song.
PostCrush
Kiwi Lollipop (K-Lo) and Supernova Zap (Su-Z) used the Time Twirler in attempt to keep their performance perfect. It also trapped Sunset Shimmer in a time loop. Sunset finds the two and notices that they have the time twirler. She destroyed it just in time before PostCrush could expose not only her, but Pinkie Pie. Nobody has to be perfect, so PostCrush had Sunset and Pinkie as their special guests at the music festival.