On the season finale of Supernatural…
Dean takes on a vampire hunt, but the power of the Mark continues to fuel him. He winds up getting another hunter, Rudy, killed while saving a girl.
Sam discovers the ingredients needed for the spell to remove the Mark.
He leaves Castiel in charge while he goes off to find Dean.
Castle asks for Crowley’s help.
Dean summons Death, who reveals that he can’t kill Dean and removing the Mark would unleash The Darkness. Dean chooses to be taken away and also for his brother to be killed.
Sam and Dean fight, and Dean questions if the brothers are good.
Dean prepares to kill Sam, but Sam shows Dean family pictures and says they are good.
Dean kills Death.
Rowena completes the spell, killing the one person she loves.
The Mark is removed, but the Darkness is unleashed.
Castle is mind-controlled to try and kill Crowley, and Rowena walks away with the Book of the Damned and the codex.