I remember watching this documentary on History Channel or Animal Planet and it was about vampires, and it was shot in Romania or at least in a castle that looked like Bram Castle, it aired in the late 2000’s and I remember the host talking about mosquitoes and similar parasites and there was a twist in which the host turns out to be a vampire.
Could it be “What We Do in the Shadows” it is a documentary shot style movie about vampires.
This came out before that movie, it was on Animal Planet or Discovery Channel and I don’t think I could find it on Youtube (since I don’t remember the title) but I do know that t was shot in a real castle, specifically Bram Castle (it may have been that or the castle used for Hogwarts in the HP franchise) and the documentary was about vampires.
I remember there were TWO halloween/monster documentaries, one of them was this one and the other was a History Channel one about werewolves, there was a weredeer or deer-person mentioned in that one but I cannot find a mention of it.