They were formally introduced in the season eight episode "Sounds of Silence", where the Kirin character Autumn Blaze revealed that after their anger and bickering destroyed their own village, the elder Rain Shine forced them to bathe in an enchanted river that suppressed their ability to express emotions or speak (however, "foal's-breath" flowers are able to reverse the effects).
In the final battle against the Rainbooms, the band was defeated, causing the ruby gem pendants with which they controlled the students to shatter and explode.
Later, Hydia decided to work with Queen Bumble to steal the Sunstone and use its power to direct the sun to allow plants and flowers to grow in Bumbleland, also slowly destroying Flutter Valley in the process.
Later, she and Draggle helped Hydia and Queen Bumble in stealing the Sunstone and use its power to direct the sun to allow plants and flowers to grow in Bumbleland, also slowly destroying Flutter Valley in the process.
However, the ponies, humans, Spike, Bushwoolies, Furbobs and Stonebacks defeat Hydia and her daughters again by sending them back to the Volcano of Gloom again.
Later, she and Reeka helped Hydia and Queen Bumble in stealing the Sunstone and use its power to direct the sun to allow plants and flowers to grow in Bumbleland, also slowly destroying Flutter Valley in the process.
However, the ponies, humans, Spike, Bushwoolies, Furbobs and Stonebacks defeat Hydia and her daughters again by sending them back to the Volcano of Gloom again.
He was then sent by Hydia to prevent the other ponies humans and their friends from bringing the Sun Stone back to Flutter Valley and making him not ticklish this time.
In the official IDW comic series, Nightmare Moon is shown to be a symbiotic force that convinced Luna to turn against her sister, feeding off of her insecurities to take control of her mind and body.
In the season two premiere, "The Return of Harmony", Discord's statue is on display in the gardens around the royal palace, until the inharmonious aura caused by the quarrels of the Cutie Mark Crusaders give him enough strength to break free of his prison.
After the Mane 6 destroy them by returning the Elements to the tree, Discord admits that he didn't tell this to Twilight because he wanted her to learn that even though she is now an alicorn princess, her friendship with the others will not change.
Later in "Three's A Crowd", he tests Twilight to see if she really cares for him by tricking her and Princess Cadance into finding a plant that will cure him of a disease he made up.
After he captures the non-princess ponies for Tirek, he double-crosses Discord by stealing his powers and admits that the necklace has no meaning to him, for it was given to him by his traitorous brother, Scorpan.
He then tricks the three villains into forming an alliance with each other so the Mane Six can defeat them and Twilight would have the confidence needed to succeed Celestia and Luna as ruler of Equestria.
In the season six finale, "To Where and Back Again", as an act of revenge against Twilight, whom she holds responsible for her defeat, she launches a mass invasion on Equestria, replacing the Mane 6, Spike, the Princesses, Shining Armor, and Flurry Heart with changelings.
In season nine, Chrysalis is summoned by "Grogar" (Discord in disguise) who tricks her into joining his team of villains, bent on conquering Equestria and defeating the Mane Six.
Chrysalis initially has issues working with Cozy Glow and Tirek, but she later learns to cooperate with them in order to finally conquer Equestria, steal magic, and defeat her enemies once and for all.
As punishment for their crimes, Chrysalis, Tirek, and Cozy Glow are imprisoned in stone by the combined magic of Discord, Celestia, and Luna.
In the season nine premiere, "The Beginning of the End", he is resurrected by "Grogar" (Discord in disguise), who tries to persuade him into working together with Chrysalis, Tirek, and Cozy Glow to defeat the Mane 6 and take over Equestria.
He quickly manages to defeat the Mane 6 after rallying Queen Chrysalis, the Changelings, Iron Will, the Flim-Flam Brothers, and Lightning Dust under him.
Sombra successfully retakes the empire, but Hope resents him for his decisions and informs him that she gave up her future as a princess to try and save him from his fate.
As Sombra is about to be killed by the Crystal Heart's energies, Hope uses her magic to hold his physical form together and the princesses turn him into a real unicorn as a sign of forgiveness.
In the season eight finale, "School Raze", Lord Tirek conspires with Cozy Glow all for the sake of revenge against the Mane Six, trapping them in Tartarus alongside him.
But after suffering from Pinkie Pie's antics, Tirek reluctantly helps them escape and Cozy Glow is defeated, imprisoned in Tartarus alongside the evil centaur.
In season nine, Cozy Glow and Tirek are freed by "Grogar" (Discord in disguise) who tricks them into joining his team of villains, bent on conquering Equestria and defeating the Mane Six.
Tirek initially has issues working with Cozy Glow and Chrysalis, but he later learns to cooperate with them in order to finally conquer Equestria, steal magic, and defeat his enemies once and for all.
In season nine, Cozy Glow and Tirek are freed by "Grogar" (Discord in disguise) who tricks them into joining his team of villains, bent on conquering Equestria and defeating the Mane Six.
Cozy Glow initially has issues working with Tirek and Chrysalis, but she later learns to cooperate with them in order to finally conquer Equestria, steal magic, and defeat her enemies once and for all.
Over the course of the film, Sunset is ultimately the one who helps to keep the friends together as the Sirens' spells begin to affect them and assists them in the final confrontation, gaining a half-pony form in the process.
After the Dazzlings are defeated, she becomes a backing vocalist and leading guitarist for the Rainbooms, the band the Mane 6's human counterparts formed for the musical showcase.