It's shadowy-wing-claws look otherworldly and incredible, even the small glimpse of them present. The transition between white, black, red, and back again is a little disturbing--and so very fitting. The face is terrifying.
And the gold--oh dear Arceus, what have you done? I will never again see Giratina without imagining ancient and unknowable scripts written upon his body. That was an absolutely amazing touch.