Proudly presenting ..
I doubt it's authenticity for some reason. When the MAC x Hello Kitty collection was released, I jumped straight onto eBay and the MAC website to check it out. I'm not sure about the website, but I'm about 80% sure I don't remember seeing the mascara/eyeliner ANYWHERE on eBay. Same with stores, I checked some department stores here and interstate and don't recall any eyeliner/mascara. It's only started popping up on my eBay searches recently, hence I have good reason to believe it may be a fake. But there's so many sellers offering it on eBay, who knows!
I picked this up at an insane 'buy it now' price on eBay, $15.99 + free postage!
Anyway, fake or not (it looks 95% real), it's an awesome addition to my little MAC family :)