When Castiel has absorbed the souls of Purgatory, he proclaims himself a god.
Godstiel used his powers to kill many angels who had sided with Raphael. He also kills people he deems to be immoral, and acting against his will, including hypocritical clergy and motivational speakers. He performs healing miracles. As the leviathans start to take over within him, and his killing becomes indiscriminate, Castiel returns to Sam and Dean, and they help him return the souls to Purgatory.