"Melds" is a broad term, referring to a type of extreme aberration among ungulates. Every so often, a horse, deer, donkey, or similar, will have a baby so deformed the only thing it seems to have in common with its parents are its use of the same anatomical parts. The mothers have never survived the birth, even when under veterinary care. The melds themselves always seem unhealthy, often suffering from infections, old wounds that never quite heal, cysts, and boils. At the same time, they can be very difficult to kill.
This phenomena is not known to occur among any group other than ungulates, and does not happen to all ungulates. Each species gives birth to its own type of meld, so although the melds themselves seem sterile, they continue to survive as groups. The cause and mechanism of these changes are unknown.
Horse-melds are most easily identified by their large, frog-like legs. More typical horse legs sprout from their body at odd angles, only partially functional but able to help move food into their mouths, located in the center of their abdomens. Their mouths are flanked by extra jawbones, complete with teeth, apparently useless.
Donkey-melds are characterized first and foremost by bone. Their heads are bare skulls with cracked jaws spreading horizontally like mandibles; the only flesh visible is the eyes, tongue, and esophagus. They have a bone exoskeleton, almost insect-like, but with invariable fractures, infections, and growths. Each leg is split in two, so that it walks on eight bone spikes.
Deer-melds have a body plan similar to that of typical deer, but the devil is in the details. They are constantly trembling, although they are swift runners and rarely seen to fall. Their antlers curve down and forward, ending below and ahead of their mouths. Their hunting strategy is to impale small animals on their antlers, then allow them to rot, eating them once sufficiently softened. Flies can invariably be found following them, and they are always riddled with parasites.
Inspired by Pripyat Beast by Keith Thompson