Probably what I say is the best thing in the pixel art here is the lineart. Personally I believe you can add much more detail into the shading since pokemon style shading in my opinion quite basic. Try adding some fur textures onto those dog and bird sprites. As for the mew animation it is quite smooth, I love the expression and of course the lineart, now this Im going to make an exception for lack of texture since mew only has very small hair on its body.
But anyways nice sprites I hope you can put that constructive criticism to work and pop out an even more gorgeous sprite.