http://us.battle.net/hearthstone/en/blog/20073614
So what do you guys think? Imho it looks ridiculously overpowered, way above C'thun levels. Play a deck filled with Deathrattle, or play a deck with a few really strong deathrattles, and this is essentially an I-win-button unless your opponent has Molten+Shadowflame, Twisting Nether or DOOM! And even then, most deathrattles will spawn new minions, meaning that you're not out of the woods.
I guess we'll need to see more cards from the expansion before we know, and maybe cards like this is the reason for DOOM! but I don't think it's in any way strong enough to be considered a counter.