We know from Lucifer that it can't kill just five things in all of creation.
I think they are :
1. Archangels (or possibly all angels)
3. The Horsemen
4. Pegan Deities
5. Mother of All
(God and Death predate creation so i guess there is no point putting them on the list)
With this in mind why aren't the brothers using it anymore? The same goes for the knife (Ruby's). Does anyone know?
Thanks in advance!