User blog comment:Tommy,Klaus&Kol2012+/How to Kill a Levithan/@comment-168.16.130.206-20120227022020

the more I think about it, the more I think the producers are going to have the brothers accidentally release next season's villain(s) when they kill the leviathans. Furthermore, they're could be an ancient artifact/weapon that kills Leviathans similar to the colt or Ruby's knife for demons. Maybe Cas returns to give said weapon to the Winchesters.