[A bit of background info: the creature are twins, two fragments of a warrior's soul. They usually travel in hawk form, but occasionally they lust for a hunt or have need for revenge and so turn into nightmarish beasts. They belong to Kartus, a character in a book I'm writing with my cousin called "Caster's Snare".]
Dark Creature: The dark hawk melted, turning liquid as it dropped from the sky until it looked like a loose sphere of oil. Then it grew, stretched like something was clawing to get out from the inside. It solidified as it his the ground, landing firmly on four legs.
It remained dark, flecked with brick red here and there. The creature was almost equine. It had a long neck, flowing mane, long tapered ears, an elongated rounded nose. Parts of it were elegant, beautiful, even ethereal, but there was such a sense of wrongness in all of it put together that it overwhelmed everything else.
Large, scaly talons grew where hooves might have been, arched against the ground. It looked terribly unbalanced, for all that it stood steadily. It's long tail was thin and boney, like its spine and skin had extended without any muscle to pad between them. The lumpy appendage was long enough to lay against the ground, twitching sporadically like a dying fish.
The places where its muscles should have been defined were smooth, more like a sculpture than a living creature. Too-short lips refused to close around its mouthful of perfectly even, flat, white teeth, leaving it with a permanent grin out of place in its equine head. Thin patches of dark fur grew over the scaled skin covering its body. The hiss that pulled from between its teeth sounded like a nest of rattlesnakes waking as something shook deep in its throat.
Where its eyes should have been, there was nothing. Empty holes sunk into the sides of its head, but it tilted slowly towards the enemy as though it could see them.
Pale Creature: The pale hawk dove for the ground without restraint. When it hit it drove up a great cloud of ash that moved of its own violation. It stirred and twisted in on itself, tighter and tighter until it molded into something solid.
The ash-colored creature carried none of the mismatched elegance of its darker counterpart. Like its sibling the creature walked on four talons, each nearly as large as its head. It too looked vaguely equine from a distance, but it was obviously made for destruction. It was shorter than the dark one, stockier. Thick muscles coiled beneath too-tight skin, protected by thick layers of pale fur. Rings of long porcupine quills encircled the base of its neck, standing on end in agitation. Its long tail and mane looked normal until one got close enough to see the tiny spikes on every end and the way the strands writhed on their own as though struggling to get free.
When it pulled its lips back in a silent snarl four rows of sharp, pointed teeth glistened in its too-large mouth. Its hungry grin more than split its thick head in half, the lower jaw unhinging just a moment before swinging closed with a loud snap. Its long narrow ears were pinned back against its head, and its too-big white eyes shone with madness and blood-lust.