I´ve thought a lot about what´s coming up next for Sam & Dean.
Until now I have two theories and I wanna share them with you. :)
In episode 10 "The Hunter Games" we got the riddle "The River Ends at the Source".
What if the source is Lucifer and Abel was possessed by him when he gave the mark to Cain??? O____O
It would make sense. It could mean Sam is the only one who is able to remove the mark because he´s the descendant of Abel.
I also hope bro-love is the key to remove the mark. A powerful force is needed to remove it.
Sam thinks a part of that powerful force is Dean himself. A PART!!! :) So the other part could be Sam. :) The two of them is the most powerful force. ♥
I also think to remove the mark the brothers have to withdraw the deal Cain made with Lucifer.
"Abel wasn't talking to God. He was talking to Lucifer. Lucifer was gonna make my brother into his pet, I couldn't bear to watch him be corrupted, so I offered a deal — Abel's soul in Heaven for my soul in Hell. Lucifer accepted... as long as I was the one who sent Abel to Heaven. So, I killed him. Became a soldier of Hell — a knight." - Cain (S09e11)
So maybe Sam has to accept his dark side!?
It could happen because Jared mentioned at HousCon his demon side is still there and maybe we will see it... OMG!!!
Oh and then we have this spoiler here from Jeremy Carver:
I also would like to see Sam using witchcraft to save Dean. Witchcraft seems to play a big role this season. I want Sam to learn some spells like his grandfather Henry did. :3
For me it sounds like SAM is the one who saves Dean. I REALLY HOPE IT´S HIM! This time it´s his turn. Please don´t disappoint me show.