Leviathan Castiel

Leviathan Castiel is the main antagonist of the Meet the New Boss Supernatural episode, he was the first Leviathan the Winchesters faced him, as he was psychopath who liked to inflict pain on others, yet he was never seen again.

Biography
After opening the door of Purgatory, the angel Castiel gained new powers, but what the did not know was that the leviathans were inside him, and then when Castiel kills Raphael, Castiel then proclaims himself as the new god. Later when Castiel was in search of becoming a better god, but nevertheless unfortunately the leviathans took over his body before they attacked Bobby and the Winchesters. And realizing that their vessel will explode at any moment, the Leviathan Castiel then heads into a lake and explodes scattering thousands of Leviathans through the sewage and having several humans who have contact with water.