Edit: FOUND! ^^
If anyone can remember this YouTube video that was made from season 7 (at least the Leviathan part was taken from it). It was black and white video and it was a "story" of Leviathan!Dean and Leviathan!Sam. OR the whole thing was "what if" the boys actually were bloody cold killers. The video started with Dean putting the suit on and shoes and then coming down the stairs. Ring any bells? Anyone? : ) Thanks in advance!
I saw this video on YouTube some months ago. Now, either it has been removed or I.just.can't.find.it! *sad*