Sunset Shimmer

Sunset Shimmer is a female unicorn pony and former antagonist introduced in My Little Pony Equestria Girls. She is a student at Canterlot High School, a former student of Princess Celestia, and human Flash Sentry's ex-girlfriend. Following her appearance in Equestria Girls, she has since appeared in other films, animated shorts, software, film novelizations and chapter books, and several IDW comics. She is also known as the reincarnated host of Sally Sonia.

Personality
Throughout the first film, Sunset Shimmer is shown to be self-absorbed, condescending, manipulative, and dishonest. She frequently insults and belittles others and thinks little of it. According to human Fluttershy, Sunset makes life miserable for "anyone who stands in her way." As a result, most of the Canterlot High School student body is afraid of her. She is also not above making threats and blackmail in order to realize her goals.

When Sunset puts on the element of magic, she transforms into a demonic visage of herself. While in this form, she becomes more ruthless, going so far as attempting to dispose of Twilight. After she is defeated, Sunset Shimmer becomes immediately repentant and apologizes for her actions, appearing to renounce her prior dishonest and unkind ways.

In the second film, Sunset Shimmer has completely discarded her old self and starts believing in friendship, being kind toward others and befriending former enemies. She is also deeply repentant for her actions in the first film, referring to her transformed self as a "raging she-demon". However, she suffers from a lack of confidence, keeping silent in situations she feels it isn't her place to speak up and falling prey to the Dazzlings' taunting. During the final battle, she finally overcomes her insecurities and joins the Rainbooms in defeating the Dazzlings, gaining a half-pony form in the process. By the end of Rainbow Rocks, Sunset starts writing friendship reports to Princess Twilight using the book she once used to communicate with Princess Celestia.

By the third film, while Sunset has managed to fully integrate herself into the group and take mentions of what she did in the past with good humor, she also harbors a fear of losing her school's newly gained trust, and she becomes deeply depressed when she believes she has let them down, despite their assurances. She also becomes increasingly irritated by her struggles to understand how magic works in the human world, briefly snapping at her friends at one point. When the human Twilight Sparkle endangers her friends, Sunset's anger explodes as she berates Twilight for meddling with forces she doesn't understand, taking her own frustrations and self-doubt out on her. However, she immediately regrets her harsh words and reaches out to Twilight in friendship by the end of the film.

In the My Little Pony: Equestria Girls Holiday Special comic, Sunset Shimmer displays a forgiving and compassionate side when she forgives the Cutie Mark Crusaders for framing her as the rumormonger "Anon-a-Miss".

In Sunset Shimmer's Time to Shine, Sunset displays a considerable level of intelligence, being ahead of her friends and classmates in school and smart enough to develop various computer applications. Her affinity for science and research is also seen in The Science of Magic, where she explains she prefers a hands-on approach to studying magic over "studying ancient books".

Pony Form
As a pony, she is a light brilliant amber unicorn pony with a cutie mark that looks like a red and yellow sun with a yin-yang symbol in the middle of the sun. Both her mane and her tail are vivid crimson with brilliant yellow stripes. And her magic aura is a light brilliant opal (as shown in Equestria Girls).

Human Form
While in Equestria Girls and Rainbow Rocks, Sunset Shimmer wears a black jacket that goes straight to her waist, an orange skirt with a light purple and a bright yellow stripe on the left side of her, a purple no-sleeve shirt with her cutie mark on the front of it, and black boots with fancy markings of purple on the front. In addition, she still has the same vivid crimson with brilliant yellow stripes hair style, but with no tail, and her skin as a himan is light amber instead of light brilliant amber.

But in Friendship Games, she wears a new black jacket (which also has bright orange-yellow 'V' shaped upside down on the shoulders) that goes up to her chest, a blouse that is light auqa with a brilliant bright yellow skirt, dark aqua pants that cover her legs (because her legs showed when they were in Equestria Girls and Rainbow Rocks), and new pairs of black-grey boots with buckles around the ankles and the same bright orange-yellow 'V' shaped upside down on top of the boots.

Daydream Shimmer Form
In this form, she is called Daydream Shimmer, and from the beginning, her hair is flying up in the sky and her eyes are marked with dark vivid crimson from her left eye, across her nose on her face, and at the right side of her right eye. On her dress, it is shown to be a bright white with a cloak that looks dark pink. Her boots are dark golden orange with her cutie mark on the top of her feet on each boot. Around her neck and arms show a collar and armbands that have her cutie mark on the front of her neck and in the middle of her arms. Last, she is wearing fingerless-gloves where she can control the magic from.

Trivia

 * She is the first major female antagonist in the series who is not a monarch, the second being the Dazzlings and next Starlight Glimmer, Principal Abacus Cinch and Midnight Sparkle. Notable, none of Equestria Girls Villains are monarchs.
 * The way Sunset Shimmer is defeated is similar to Nightmare Moon.  It is even possible that her demon form is the embodiment of her evil side, much like Nightmare Moon is considered the embodiment of Luna's jealousy, exorcised by the Elements of Harmony and purifying both (though it's also believed that the cause of Sunset's redemption was horror at what she became). It also was an homage to the first defeat of  the villain in the series.
 * Before her redemption, she shared similarities with most of the  main villains in the series so far: Nightmare Moon (past with Princess Celestia, seeking to rule over Equestria, and defeated in the same way by Twilight Sparkle), Discord (breaks friendships for the fun of it), Queen Chrysalis (manipulative, power-hungry, resorts to brainwashing), King Sombra (uses evil magic, seeks to conquer Equestria), and mostly Trixie  (arrogant, insufferable, uses the power of a magical artifact that gives her immense power at the price of her sanity). She is also similar   to Discord in that one of the Mane Six's actions was able to reform her; Fluttershy for Discord and Twilight for Sunset Shimmer.
 * Rebecca Shoichet, who does Sunset Shimmer's voice, also does the singing voice of Twilight Sparkle.
 * Sunset Shimmer can be considered an evil counterpart of  Twilight Sparkle due to how many similarities they share. Some fans have  speculated she is what Twilight may have become had she not discovered friendship and its meaning.
 * After starting to believe in friendship, Sunset Shimmer acts  more like Twilight Sparkle, being the peacemaker of the group, having insecurities, and developing a worrisome personality. A difference is that Sunset is quite patient with the group's rage while Twilight is quite temperamental with hers.
 * Sunset Shimmer is the first main villain of a part of the series written by Meghan McCarthy who unambiguously survives. Lord Tirek and Adagio Dazzle follow.
 * Sunset Shimmer has many similarities from Golbez: (Became a  very misguided and confused antagonist at debut, Once was a Clad in Dark: Her she-demon self, Felt horrified of her actions and feelings of hatred after snapping out of her misguided ways(cried about it after and  because of her demon transformation), Becomes a caring, self-sacrificing, and empathetic friend, Unforgiven by everyone except Twilight's friends after the atrocities she made in her debut, Pays for her crimes by learning about friendship, relates to Twilight as she once   was Princess Celestia's student, Twilight's friends forgave her after changing her ways, Found hope for the Rainbooms to defeat the Dazzlings,   Everything she did was to save Canterlot High but became oblivious to the Dazzlings' evil schemes, Gave words of wisdom to her friends(but doesn't realize it), Made sure that her friends are safe, Had to live up   for her crimes, Assisted the heroes and worked with them(Joined Twilight unlike Golbez in Dissidia), Swore to defeat the Dazzlings after   the atrocities they made at Canterlot High, Summoned powerful magic to defeat the Dazzlings (god-like magical alicorn because of Sunset's singing), Saved the day in the end, feels sorry for the Dazzlings, has to work on friendship, Had to do something about her past(erase it). The   only difference is that she sums up Garland in Final Fantasy perfectly during her debut in terms of actions and personality
 * Demon Shimmer, "she-devil" alter-ego of Sunset Shimmer in her  demon form is one recurring symbol of "Equestria Girls" - being the real  villain in the first movie like Nightmare Moon,   she was then the reason of Sunset Shimmer being an outcast among the students in "Rainbow Rocks", also, she is mentioned and seen in clip "My   Past is Not Today" at evil of Sunset. In "Friendship Games" her picture, along with the Dazzlings, appears in Rainbow Dash's song to cheer other up. Also, Midnight Sparkle is obviously has the same nature as Demon Shimmer, being the user of twisted power of the Friendship Magic.
 * Sunset Shimmer along with the Dazzlings are the only major antagonists to not appear in the two-part Season 5 final "The Cutie Remark".
 * Sunset Shimmer's voice had just sounded similarly like Penny's voice.