On my AU, changelings are descended from ponies, so their base form still is very similar to ponies’, even if their similarities are mostly on surface (since they lay eggs, they don’t have nipples and their chests are covered by a part of the exoskeleton), and their exoskeleton, while not as hard as bone, still is strong enough to hold them up. their joints and bellies are comprised of softer layers of tissue.
Changeling diet is based on magical energy (the most ‘nutritious’ for them being love, with negative emotions having practically no positive effect on that front) and normal food, with a dearth of either of them affecting their ability to transform, and at points, making their exoskeleton harder, darker and more brittle, along with other assorted health problems that come with starvation.
One day to finish this, decided to try to improve the shading.
Pose and tree trunks taken from this 1891 piece by Apeles Mestres