You always start off with the gem in my experience. Secondly it's the size that it's undoing. Cat's can't generally scratch behind their back so good so you should try a levitation spell to get between the wings while someone destracts it with a cat toy the size of a bus or something. Once there, just hold onto some fur for a while to catch your breath then pull out the nastiest staff in your arsenal. I would also worry about what a cat that big eats as well as the cat.