09x11 “First Born”
10x21 “Dark Dynasty”

I just cannot shake the feeling that all of it is connected. Somehow… I mean on the one hand we have the trinity with Lucifer/the blade/the mark (the one who bears it), but then again, the way Dean reatced to the book it reminded so strongly of the way Cas resonated with the angel tablet and the way Sam resonated with the demon tablet, so it could also be the book (as the human tablet)/the blade/the mark. It’s probably not it, but I just felt reminded of Cain’s words when watching the promo.