This ended up being a demon like creature, but with a large rocky growth on its back, while the muscles for the legs and arms are functional the design as a whole has flaws that would need a full redesign . The tusks and horns , whilst imposing are impractical, and the large back serves no purpose.
I really like this design , particularly the layered face , with an oversized head. It seems intelligent but dark and wholly unsettling. The design could be refined and iterated upon to make it flow better , removing the saddle and making it more of a slow lumbering beast than a steed. The multiple horse legs dragging the body along are a cool design but the hooves could be replaced with something with more traction or potential to to be used offensively or to feed itself.
I’m getting a very dark souls vibe from this design , reminiscent of the gaping dragon, with one head on the top with its own individual mouth , and then a huge maw where it’s chest cavity used to be , and a bubbled veiny tail