Slaypire

"A creature like you cannot be allowed to survive."

- D'Hoffryn

A "slaypire" was the result of a Slayer being turned into a vampire.

Known cases

 * Yuki Makimura was the very first Slayer to ever be turned, her sire being the Master. As a result, the Watchers Council omitted her from their records entirely, though they neglected to cover up the two missing years in the Slayer timeline.
 * Buffy Summers was temporarily transformed into a vampire when Billy Palmer's astral body caused people's nightmares to manifest throughout Sunnydale.
 * Simone Doffler enacted a plan to turn the Slayers working under her into zompires in the hope that, by becoming one herself, she would be able to retain her mind and kill Buffy, one such victim being Tessa Freer. She eventually succeeded in her efforts by traveling to the Deeper Well and awakening the Old One Maloker, the progenitor of the vampires.

Characteristics and Traits
Slaypires went through the same psychological and physiological changes as regular humans did, retaining their memories but becoming undead and evil. However, Buffy did not when becoming a slaypire (probably so that she suffer her nightmare made real).

The turning granted them physical abilities superior to conventional vampires and Slayers, but also the conventional vampire weaknesses and limitations.

When Buffy was a slaypire, she fought off the Ugly Man successfully, despite being unable to take him before being sired. Moments after becoming a slaypire, Simone could easily overpower Buffy, a Slayer of greater power and experience.