Sonata Dusk

"But, we can get lunch after though, right? It's Taco Tuesday!"

- Sonata Dusk

Sonata Dusk is the tertiary antagonist in My Little Pony Equestria Girls: Rainbow Rocks. She is a backup singer in her band the Dazzlings, rivaling the Rainbooms.

Role in the Film
The Dazzlings, including Adagio Dazzle, Aria Blaze and Sonata, appear in My Little Pony Equestria Girls: Rainbow Rocks as the main antagonists.

In the film, Sonata and the other Dazzlings are introduced in the human world. They are sirens from Equestria who were banished to the human world by Star Swirl the Bearded. They are first seen in a café causing tension between the patrons, and Sonata briefly argues with Aria Blaze. She and the Dazzlings later convince the students with their music to turn the friendly Mane Event into Battle of the Bands.

Sonata and the Dazzlings use their siren's songs to control student opinion and advance through the competition bracket.

Sonata and the Dazzlings are eventually defeated and the gem pendants with which they controlled the students are destroyed. As a result, they are unable to even sing and re-cast their spell. Their inability to sing leads to them being chased off in disgrace as the enraged students booed and pelted them with fruits and vegetables.

Personality
She is shown to be somewhat air-headed, distracted, ditzy and carefree - she is clearly a follower with absolutely no capacity for leadership. Some examples of her shortcomings include: not picking up on Adagio Dazzle's sarcasm when she says she "loves" the human world, speaking candidly with Sunset Shimmer about her friends' true nature (nearly blowing their cover) and showing herself to be more focused on getting lunch than on their plans. She tends to forget the group's main objectives, perhaps hinting she is not as obsessed with power as Adagio and Aria are. She frequently argues with Aria Blaze over trivial matters. Nevertheless, she still shows a noteworthy level of cruelty, as she appears to take pleasure in belittling Sunset Shimmer and as she never seems to be bothered or at least show remorse when it comes to putting Adagio's evil plans into action. Plus, she acts more evil and serious during the final battle of the film.

Appearance
In Equestria, the sirens' appearance is similar to that of a dragon, pony, and sea creature hybrid. In the human world, the Dazzlings are shown to possess translucent wings in their anthro forms, unlike their true forms. Their siren forms are summoned as astral projections from their pendants and used to weaken the Rainbooms.

Aside from flashbacks, Sonata's true form is never physically shown in the film, but she and her fellow band members gain pony-like ears, extended ponytails, and translucent wings. They also summon astral projections of their true siren forms from their pendants.

Trivia

 * Flashbacks reveal their original siren forms in Equestria where that of Hippocampus.
 * A lot of fan art erroneously depicts their alternative forms as mermaids, being the most common form for sirens.
 * In music terminology, a sonata is a piece of music without vocals.
 * Her last name, Dusk, may be a pun of sort: she is indeed the dimmest of the three Sirens.
 * She is heavily associated with her "Taco Tuesday!" quote in the fandom.