User blog comment:ImperiexSeed/The oldest being, archangel or leviathan?/@comment-203.81.71.69-20140507062832/@comment-3481504-20140520080227

I'm no where near biasing anything on this. Despite the peculiarity of your belief, retecon is the conflict in a lot of areas because Kripke aggregated his story which culminated at "Swan Song"-so Leviathan might've not existed in his mind. According to Castiel, the only limited being (therefore not referring God or Death) who can best and kill Lucifer is Michael. Also, to point out, Crowley was brave enough to try an negotiate with Dick, but didn't dare enter Lucifer's presence.