“It’s that darkness that Deaton warned us about at the end of last season,” O’Brien says. “For Stiles in particular, he’s an interesting candidate for a host. Me, Scott, and Allison have very vulnerable minds at this point because we left the door open for what we did to sacrifice ourselves for our parents. We are prime subjects for any sort of spirits and evil to come in and have a great time.”
(...)
“Being the human, he’s very vulnerable, as he’s always been. But I think now that it’s going to be a lot about Stiles kind of dealing [with the fact that] he’s not safe. It’s kind of that thing with the superhero’s girlfriend.”
(...)
“We were butting heads a lot last season because of what [the sheriff] didn’t know, and he could just tell I was keeping something from him, and it was killing me and making me act weird around him. That was disrupting our relationship. Now Stilinski understands why it took Stiles so long to tell him, why he chose the time to tell him that he did, and I think it’s going to bring them closer, strengthen their relationship, for sure.”
Source
Oh, man. I'm loving these spoilers! Is it January yet? *bounces*