Yeah, looked up the Bluespawn Godslayer and it's kinda on-par, visually. However, if I may? I'd fit it with the half-red dragon template (MM1), for the fiery hue that your sample has, as well as the half-iron golem template (MM2), for the large and bashy mechanical arm. Finally, to replicate the "arrow launcher arm," I'd recommend looking into the Maug grafts, at the back of the Fiend Folio, as there's one called a "Stone Spitter" that acts like a magically-enhanced railgun, but there's nothing to say that it can't look exactly like the one you showed us, and uses arrows instead of rocks or stones.
Hope this helps!
p.s. If you want to be extra sneaky, since the front of the beast is a pale, icy-white, you might even get away with saying that it has Cold Resistance of 10 or 15 - yes, even with it's red-dragon status - but that might be either cheesy, or awesome, depending on how hard you like seeing your players work!