Snow White Hills Blood Bowl Chronicles

The history of these creatures is obfuscated by the centuries and by the inherent stealth and secrecy of the Undead, but two main theories prevail as to their origin. The first is that even when alive they always fed upon others, much like larger cousins of the gnats and mosquitoes that plague travellers in the summer twilight. In this version of events, the first Vampire Bats fed upon a sleeping Vampire by accident, assuming him to be a living Human; perhaps he had recently fed himself, and still glowed with the warmth and blood of his victim. The other theory posits that they were the creation of a powerful Necrarch Vampire or perhaps a Necromancer, who desired a powerful flying strike force to supplement his Undead legions. In either case, the biggest mystery is whether they reproduce like living animals—making them the only known Undead to do so—or whether they may only be created by some other means, perhaps the sorceries of another powerful master of Undeath.: — Heinrich Malz, High Priest of Verena, Nuln.