every fking game im tired of seeing them. Warwick has far too much rotational power and map pressure early it needs to be cut down or his late game needs to fall off harder. Nasus is self explanatory he is literally a god after 400 stacks or so like do your job riot pls
im shocked there wasn't an additional 
skin this patch as well also aids that should be nerfed.
It's the Year of the Dog. Pretty much everyone and their mother knew either Warwick or Nasus were getting skins for Lunar Revel.
I'm fairly certain it's just based off of the popularity of the champion. That was quite literally the reason they gave for Lux's Lunar skin.
Added - Forgot to mention, they're Lunar Day skins. Year of the dog. They're dogs.
It's been a meme for a while that they often release skins for strong champions right before nerfing them. Since meta champions are popular, they sell more skins, and a few weeks later they nerf them. Whether there are any amounts of truth to that meme is hard to tell, but it sure seems like there is a correlation.
Also year of the Doge as other said, which also confirms that Lux is a b*tch :D
But 
got a nerf and has been untouched. The skin argument is stupid.
