Which X-files episode had a vampire?

The episode called "Bad Blood" (Episode 12 of Season 5) is about vampires. It's one of the more comedic episodes, as opposed to the more serious episodes.

Also, the episode titled "Three," which is Episode 7 of Season 2, is about vampires. Actually, Mulder ends up having an affair with one of the vampires (played by Perry Reeves, who was David Duchovny's real-life girlfriend at the time).