Hearthpwn

His effect is really powerful but (imho) not outside the realm of possibility, with his cheap mana cost i could definitely see Chromaggus seeing play (if this is in fact a real card).  That being said, this card has some serious weaknesses that keep it in check and if this saw wide spread play or even became key in a powerful deck it would make priest a lot more viable (they have a decent amount of tools to get rid of him easily).  

It's also interesting to note that Chromaggus + Mind quickening gem (if this leak turns out to be real also) will be a pretty nice combo.