The Dazzlings

Introduction
Adagio Dazzle, Aria Blaze, and Sonata Dusk are collectively known as the Dazzlings. As young merponies, the three found a trio of magical jewels hiding in a treasure chest in the sea. After putting them on, they went on to hypnotize the ponies of Equestria with their music, causing chaos and evil wherever they went and feeding off the resulting negative energy.

Life as humans
Starswirl the Bearded later banished them to the human world, and they arrived during the time of Ancient Greece, where they met Odysseus.

In the Victorian era, the trio were playing a series of shows at the Savoy theater when Sonata was struck with cholera. Gem, who had time travelled to this time and place, took Sonata's place on stage and the concerts were successfully completed. A few years later, the trio moved to the United States, where they supported Union troops as they fought in the American Civil War.

They arrived at Canterlot High in time to cause an enormous amount of chaos, turning what had been a musical showcase into a Battle of the Bands and temporarily splitting up Gem and Raven. They were eventually defeated, and robbed of their hypnotic singing powers forever. They were also made mortal.