Fell Bats are what Sylvania's bad earth makes of its wildlife: bats grown huge and vicious in warpstone-tainted caves, ruined chapels, and the towers of Drakenhof itself. They answer the vampires' will as hounds answer a huntsman, ranging far ahead of the undead host to snatch messengers from the roads, blind sentries, and tear at the crews of war machines before the first grave has even opened.
The counts value them less as killers than as heralds and eyes. A vampire lord can borrow the senses of his bats and see the night as they see it, and Sylvania's borders are watched from above by wings that never entirely leave the sky. The border folk read the omen correctly: when fell bats circle a village at dusk, the count already knows everything he needs to know, and the army is already on its way.