A shape-shifting quadruped species, feeding on the emotion of love, which is said to have successfully infiltrated the Equestrian government in the Golden Age, with the goal of maximizing love production for their own nourishment. The species was apparently greatly reduced in numbers during the Catastrophe, as the result of their central hive-mind being destroyed. In modern times, the open and peaceful existence of changelings is known; it is generally assumed that there are also a number of clandestine changelings, but reliable information on that topic is scarce.
After PRPG2
Element use here (working on this, but wanted to save what I had)
Equus - Rainbow Changelings
under construction
Exile
Those changelings who chose exile were, as the Elements said when offering the choice, banished to a far-distant dimension devoid of other life. There, by the physics of that place, they could live without preying on others, but neither were there any beings for them to be a threat to. There was nothing there that could threaten them, and sturdy barriers around the dimension against escape or incursion. In particular, the Elements took great care to ensure that the exiled changelings could not get back to Equus's universe.
The Colony Ships
The two sister ships of the Harmony that were able to escape Equus are out-of-universe known to have survived their flight from the planet, though their locations are unknown and contact has not yet as of PRPG3 been reestablished. Due to the nature of the magic they used to escape, they could be reappear more or less anywhere in the universe at more or less any time after they departed. Little has been defined about them overall, but it was desirable that some information be given her on the fates of the changelings aboard.
Luna's Changelings
Luna, while upset at the changelings' actions, was wiling to hear them out and negotiate, in large part due to her past with them and role as their creator. Not wanting to destroy them and knowing how useful they could be to her ponies but also unable to truly trust them and unwilling to demand that her ponies do so, she worked with them to alter their nature, as Chrysalis had long ago, this time to give them a ponylike inherent regard for non-changeling sapient life. This change made, the changelings continued among the people under Luna, beginning to repair their relationship with her and them.
Celestia's Changelings
Celestia quickly killed all of the changelings on her ship, her past experiences with them being overall far more negative than Luna's.