after some minimal sketching, a 3d concept blockout sketch (just blender and cycles viewport20 passes in two seconds on my shitty GPU for a fast lighting preview)
Maybe you could give the creature wiry, skinnier, with a slender waist like a sighthound, maybe give it a more grim and surreal appearance. I think you also should keep the bony beak you made on your first sketch.
I'm really digging where this is going, your sketches have a lot of character to them and the style's got a really cool, grungy sci-fi look to it. I really like the armored-up rider, but it would be cool to see more more of the deer-skull forms on the helmet you had in your lower silhouette, something really cool and…