With Castiel’s blood already secured, the brothers turn to Crowley. He agrees to help but demands they find the first, as his own blood is a "last resort" that could be used against him.
In the penultimate episode of Season 7, Sam and Dean Winchester race to assemble a powerful weapon to take down Dick Roman and the Leviathans. Following instructions from the Word of God tablet, they must combine the bone of a righteous human with the blood of three "fallen" beings: a fallen angel, the King of Hell, and an Alpha monster. The Quest for the Alpha's Blood [S7E22] There Will Be Blood
While the brothers are away, Bobby’s ghost continues to struggle with his mounting rage. With Castiel’s blood already secured, the brothers turn
His presence is marked by icy mirrors and flickering lights. Following instructions from the Word of God tablet,
Kevin Tran remains a prisoner, forced to translate the Word of God under the threat of his mother’s life.
While Sam and Dean have two of the three blood samples, they discover Bobby has vanished, and their only remaining ally, Crowley , is now in the enemy's hands.