Okay, so they established in On the Head of a Pin that only angels can kill angels. Since Lucifer is technically an angel, how can Dean kill him? Unless "stop" doesn't mean kill. I've only seen the finale once so my mind is foggy. (And my personal opinion is that Dean won't "stop" him anyway and maybe Lucifer will just be cast away/rebound. I dunno. Unless he really wants zombie!Paradise. Maybe Lucifer be defeated some other way.)
Let's assume it means kill. I don't subscribe to the theory Dean is an angel (and I don't want him to be either.) Does that mean someone like Castiel would have to do it? But if an angel does it, that sort of negates the fact Dean is supposed to do it. Unless Dean will eventually get possessed by an angel (which I don't think he could anyway) and seems like cheating.
Or maybe Lucifer doesn't quite qualify as an angel anymore.
I don't know. I'm sure Sam will factor into everything. I'm just wondering if I missed something. I haven't been super attentive this year. I'm just thoughtful this morning. What do you think?