User blog comment:Fusedtwilight/Possible Season 11 Plots/@comment-78.145.128.117-20150525133803

In regards to the second theory, while I think they might bring Michael and Lucifer back for the fight against the Darkness in Season 11, I doubt Lucifer has the Mark since he gave it to Cain for two reasons:
 * 1) Because if Lucifer did still have the Mark, then shouldn't the Darkness have remained imprisoned when the Mark was removed from Dean since there would have still been one copy of the Mark in existence?
 * 2) We never saw the Mark appear on either Nick or Sam's right arm in Season 5 when Lucifer was possessing them.

As for the fourth theory, Team Free Will will probably have to rely on finding another source of info on how to stop the Darkness, since as I understand, the Book of the Damned's secrets are how to undo curses rather than create them.