Oh… Well… They're based on Slavic Strigoi or Nosferatu…
They have superhuman strength, stamina, agility, durability and a healing factor, can turn into a wolf, a raven, a horde of cool, nasty things like sneks, lizards, spiders and bats, or a puff of smoke. They can hypnotize with a look.
They are annoyed by sunlight, and if they are BOTH decapitated and impaled, they turn into the horde of nasty things to regain their strength. Killing EACH and every one of the creepy-crawlies will destroy the vampire. They can be killed by fire…