User blog comment:Noctosphere/We finally get a Human as a big bad. Your thought?/@comment-74.58.154.192-20160602204901/@comment-34326521-20160604054657

The perfect human Big Bad, IMO:

Someone like Cole (found out about the supernatural world), who holds a position of power over at the FBI or other such organization (but isn't at the top) and wants Sam and Dean arrested (maybe killed) before they do any further harm. Sam and Dean won't kill them, since they're human (and in the FBI), but the opposite isn't likely to happen.

Or maybe the writers could go with the "government knows about the supernatural; secret task force to study and contain threats" cliche and get those guys on Sam and Dean's case, though that would be somewhat boring.