season 9 finale
After Dean attacks Gadreel with the First Blade, Sam and Castiel lock him in the bunker's dungeon out of fear of what the Blade is doing to him. Gadreel reveals that Metatron intends to convert humanity into following him instead of God. As the power Metatron draws from the angel tablet makes him unstoppable, Gadreel and Castiel decide to infiltrate Heaven to break the tablet and his power, while Sam goes after Metatron himself. Dean summons Crowley, who helps him escape and start tracking down Metatron, but Dean has Crowley leave after Sam agrees to help him. The two track down Metatron, but Dean proves no match for him and is fatally wounded. In Heaven, Gadreel and Castiel are found out and locked in Heaven's dungeon. Gadreel sacrifices himself to free Castiel and convince the angel Hannah to help him. Castiel finds and shatters the angel tablet, reverting Metatron to a regular angel and forcing him to flee before Sam can kill him. Metatron confronts Castiel, arrogantly announcing that he will rule both humanity and the angels who he sees as beneath him, not knowing that Castiel is broadcasting his words to every angel in existence. The angels turn on Metatron, overpowering him. Castiel locks Metatron in Heaven's dungeon instead of killing him. The other angels look to Castiel as their leader once more, however he would rather be a regular ange
l he went to the bunker to tell bella that he is an angel again and they kiss and that He is faced with the fact that he will die soon unless he replenishes his grace and bella looks sad . Dean succumbs to his injuries and dies; while Sam tries to summon Crowley to make a deal to resurrect him, Crowley visits Dean, revealing that the Mark of Cain won't let go of him. Crowley tells him about how the human Cain had been transformed into a demon by the Mark upon his death. He then places the First Blade in Dean's hand, and Dean opens his eyes, now a demon himself.