The Entity\n\n The Cosmic Entity might be the most powerful Supernatural monster in history, but there is not enough known about it to rank it very high on this list. The Entity predated God, the Darkness, and Death. However, the full power of the Entity is unknown, as we still don't know what its specific powers are yet.

The song that Dean is humming to calm himself down on the plane is called "Some Kind of Monster" by Metallica.