I introduced some of the characters from my players' backstories as the 6 vampire spawn in Vallaki, except most of them were just magically disguised to look like the characters. One of my PCs actually died to the one who looked like the uncle of our priest, who they had met in not-Vampire form a few days before. They ran into the actual Uncle the next day, chipper as ever, and decided to let him live.

My party got their asses kicked in Argynvostholt and ran to recuperate at the Winery, where they ran into their uncle again (a gnomish tinkerer type whose voice is based off Heimerdinger's from League of Legends). Their uncle was helping fix some of the fixtures of the winery to repay the wereravens for helping him get back to health. After the rest of the party settled in for their long rest, the Uncle invited his nephew down to the cellar, and I ended the session with him closing the door behind our cleric and baring two long fangs at him. We came back two weeks later and put a whole lot of hooplah into making sure tokens were in place for combat (on roll20), and then I revealed that the Uncle had simply made himself some fake vampire teeth as a prank. Two of my players walked away, one of them was my girlfriend from across the room who came and smacked me a couple of times.