i hope it's castial

Bobby's ghost?

Of course

I don't think it's Cas. For starters, he doesn't strike me as a beer drinker. That's all Bobby. And Bobby was only given two options: move on, or be stuck as a ghost. Since we know Bobby is coming back (at least, for a little while), and we don't know what he chose...

Plus, there was that picture Misha tweeted. He hasn't confirmed or denied that it was Cas, but I'm pretty sure it was. If that's the case, then it couldn't have possibly been Cas.