He can transform his body into that of other ponies, fly and use magic. Has large fangs, and slightly insectoid features.
This race feeds off the love of others, changing onto close individual's identities for doing that, usually. 

He was accustomed to it, a bit too much, causing him to doubt if he was being his real self or just acting like someone else to blend in. He's kinda unstable, not knowing much about how to interact with others because of the evasive nature of his people's lives.

Changeling pony (season 2 lore only)

She's a pony, unicorn mare, lilac coat, straight bangs, blue hair with strands of purple and pink. Purple eyes

Prone to get stressed, likes neat things, planning, and just have everything in order...
It can cause her to spike into anxiety if things aren't going to her plan and schedule, even as far as causing some hallucinations... And then she's going to try make things go her way to follow her schedule. By any means.

Lesson zero ep inspired

Everyone's eyes were on his rival Red, taking the attention, being left in his shadow, because despite all the effort, achieving to be the best, Red took that spot too, alongside his grandpa's attention.

Probably feels like no one recognizes his achievements, used to have big ego, after his Raticate's death in a pokemon battle with his rival, he snapped and went for revenge, filled with depression and anger.

Image by NaginoKi429/Akuta_krps

A pink coated pony with fucsia straight hair, and light blue eyes.
Kinda erratic sometimes, can become mad easily, and doesn't like when others leave her behind or out. Specially ones she considers friends.

Will act like it doesn't hurt her, smiling as if like it's a great thing that happened to her. Can be very crazy and unstable, talking and referring to inanimate objects as "true" friends.

Might jump to drastic conclusions when not finding clear answers about things. Dislikes excuses/lies.