The Changelings are the secondary antagonists who first featured in A Canterlot Wedding - Part 2, and are the minions of their ruler Queen Chrysalis. They are shown to be pony-esque creatures that resemble bugs and have the ability to change their appearance into any other form presented to them at any time. They do not have cutie marks.
In A Canterlot Wedding - Part 2, the changelings are shown breaking the magic force field around Canterlot, and later terrorizing Canterlot, as well as taking the form of the main six ponies and engaging in battle with them. They are soon sent far away from Canterlot by Shining Armor and Princess Cadance's combined magic, along with Queen Chrysalis at the end of the episode.
In Do Princesses Dream of Magic Sheep?, Rainbow Dash's dream has her fighting changelings, which she says is her favorite dream.
In the comic The Return of Queen Chrysalis, they return, having survived their fall, and kidnap the ponies of Ponyville while disguised as animals, taking the ponies' places. The Mane 6 eventually fight them in a similar style to before, and take out a few of them before Pinkie Pie traps the rest in bubblegum using a cannon. Spike is left in charge of the captured changelings as the Mane 6 set out for the changeling kingdom, where Chrysalis is holding Apple Bloom, Sweetie Belle, and Scootaloo. Some changelings are sent to manipulate the Mane 6 by separating and impersonating them. In the end, they are defeated by Twilight along with Chrysalis and imprisoned by Pinkie Pie in their castle, entranced by a costume she set to ask riddles and sing endlessly to them.
However, recently, on page 11 of Friends Forever Issue #8, a sign under the Mount Monument observation deck reads "Sign the petition to add Queen Chrysalis to the monument" and bears Chrysalis' fresh signature, which in turn strongly suggests they have since recovered and are back to plotting and causing trouble for Equestria. Chrysalis's Fiendship is Magic issue has her and her changelings escape and they are once again at large.
(It should be noted that it is up to the fans to decide for themselves whether the comics are canon)
Their interest in taking over Equestria is explained by their source of nourishment being true love, and that Equestria has "more love than [they] have ever encountered."
Queen Chrysalis and the changelings may be based off of Sinisteeds, dark, horse-like creatures who thrive on feeding off of love and emotion in the novel Gossamer by Lois Lowry.
The changelings are shown to be evil, mischievous and cruel individuals, though as only the Queen and her army has been shown, it is uncertain if this can be said about all changelings as a whole.
- When the changelings shatter the barrier around Canterlot, it looks similar to when Voldemort destroys the barrier around Hogwarts in Harry Potter and the Deathly Hallows Part 2.
- The way Chrysalis and her army of changelings are sent flying into the distance echoes Team Rocket "blasting off".
- Changelings slightly resemble Thestrals from Harry Potter
- The comics depict the changelings (or at least three of them, one with armor) landing in the same area as their queen after their defeat in A Canterlot Wedding. However, in the episode only one changeling was shown flying in the same direction as her, as they are scattered in all directions.
- They are based of the original Changelings from folklores
- There are theories that duplicate background ponies seen throughout the episodes are actually changelings in disguise.
- A changeling is seen in the audience at Cranky and Matilda's wedding in the 100th episode, and was confirmed by the writers to be a friend of Matilda, indicating that either some changelings are good and do not follow Chrysalis, or that some survived their fall and changed their ways.