I can imagine the difficulty with showing little details with a small resolution. For the backsprite of the original Kyurem forme, I don't think it was a good idea to copy-paste or replicate it's left wing. The perspective is turned off because of them looking identical. You should try respriting the opposite wing.
I do agree with you, i have redone the backsprite and the wing is now how it's surposed to and it looks much better. Thank you for pointing out the little problem.