Seems kind of lame that switching to Shadow Kayn causes you to gain bonus damage, that just so happens to be MAGIC bonus damage. Riot plenty well knows shadow Kayn is gonna build full armor pen. So is this just some odd way of Riot being annoying, or something?
If you really think his passive would do too much damage, then why not just reduce its damage? Making it magic as a strange and bazaar method of nerf, I donno, it's just weird. I like everything to be neat and tidy, and seeing magic damage on my full armor pen build just doesn't look clean.