In the second half, Dean begins searching for both Gadreel for revenge and the First Blade to kill Abaddon with the help of Crowley. Despite being warned of terrible repercussions, Dean takes on the Mark of Cain in order to be able to wield the First Blade. After healing Sam completely, Castiel begins a search of his own for Metatron, believing him to be the key to reversing the expulsion of the angels. Metatron begins trying to unite all the angels under his rule while Castiel leads other angels against him to retake Heaven. Eventually Dean kills Abaddon and Castiel defeats Metatron after a repentant Gadreel sacrifices himself to let Castiel confront Metatron directly, but Metatron kills Dean, causing Dean to become a demon due to the influence of the Mark of Cain.