Never mind, I think I figured it out. That corpse in the magic circle at the end, that corpse that's holding the talisman, I think that's Cyrus's corpse. I thought it was someone who was murdered 100 years ago by Carno, but now that I think about, it makes sense that it was Cyrus. Cyrus jumped across that hole in the floor in the secret passage (that Adrienne can't cross until after Don dies) just like he jumped over to where the greenhouse was. In both places, if you go there before you need to, Adrienne says the exact same thing in the exact same way ("It's too far, that's be a long jump"). I think they even used the exact same soundbite of Adrienne saying that in both those places. And they did that for a reason. The important thing is that Cyrus can jump across both holes. So, Cyrus jumped across the hole in the floor to escape Don, and it didn't work.
Now that I think about it, Malcolm said that Gaston was buried in the tomb that's labeled as Carno's tomb (because Gaston was so badly mutilated that everybody thought he was Carno), and I don't remember any other MEN being murdered by Carno, so I guess that corpse in the magic circle couldn't be anyone Carno killed.
Then again, maybe I have it all wrong.
EDIT: Never mind again. I DID have it all wrong.
The body holding the talisman is the corpse of Carno. Remember that Malcolm says that he brought the corpse of Carno to his secret chamber. I suppose that before that part of the tunnel caved in their was something like a wall with a hidden door.