season 6

The sixth season begins a year after the Sam jumped into a cage with Lucifer and Micheal.Dean lives a happy life with Lisa and Ben. Sam mysteriously returns to the world of the living and teams up with Dean. Before Sam joins Dean ,he has been working under Samuel Campbell in order to hunt and capture alpha monsters(first of its kind) alive. Castiel is barely helpful anymore because the civil war against the archangel in heaven .They discover that Samuel is following Crowley's orders in exchange for the return of his daughter. Crowley wants to use the alphas to locate Purgatory, in which there are a vast collection of monster souls that are dead and can be used for power.

Samuel Campbell

they also fond that Castiel brought back Sam without his soul and Dean implores the help of the horseman DEATH in order to retrieve it. dDeath puts a wall in Sam's mind so that he will not remember hell. The old Sam returns with no memory of the past years. it turns out Castiel made a deal with Crowley for each of them to receive half of the souls in Purgatory.

Sam in Hell (memories)

Dean doesn't like the idea and tries to stop the duo. To get the winchesters and Bobby to slow down , Castiel knocks down the mind barrier in Sam. Castiel berays Crowley, Crowley becomes alias with Raphael and perfoems the ritual to open the doors of purgatory. It fails because they had the ake dog's blood and Castiel appears full of power from having done the ritual himself.

Castiel with full power 

He obliterates Raphael and Crowley escapes. When the Winchesters try to talk to Castiel , he reveals that he is not an angel anymore, he has become the new God.