Board Thread:False Info and Speculative Discussion/@comment-24.130.28.230-20150721180826/@comment-5690373-20150723195003

It's not clear if Mountain Ash affects all Supernaturals. In season 2 it wasn't clear wether it was going to work on the kanima and in season 3B it wasn't clear wether it was going to work on the oni or Kira.

As for Banshees being supernatural, in season 4 we had a hitlist of supernatural creatures, Banshees were on said hitlist, therefore Banshees are Supernatural. If Deaton did indeed say that ALL supernaturals are affected by mountain ash (which I can't quite recall) then we have a contradiction in the show.