Buffy DID turn into a vampire in the first season. Everyone’s nightmares were coming true, and it was Giles’ nightmare that he could fail in his duties as a Watcher and let Buffy be turned. I don’t recall any alteration in her powers; she merely suggested that they get the situation wrapped up fast, since she was getting … hungry.
I did think of “Nightmares” but I disqualified it on the grounds that it was merely Giles’ nightmare, and did not actually happen insofar as Buffy was not actually vamped, etc., so I don’t think that can necessarily be relied upon to describe what would happen. For one thing, Buffy was clearly not evil. That raises an interesting point: would a VampSlayer not transition to evil-being as well as a regular person?
It wasn’t Giles’ nightmare that Buffy would be turned, that was Buffy.
When Giles, Willow and Xander were in the graveyard and came across Buffy’s grave, someone asked who’s dream this was. Giles said it was his and that he had failed in his duty to protect her. When Buffy rose from the grave in vamp face, Giles said something to the effect of “I never knew you dreamt of becoming a vampire.”
A slayer is imbued with the power of vampires. That’s how they made the first one, remember. My guess is that there would be no combat differences whatsoever; only the undead stuff. (Sunlight, immortal, holy water, yada-yada-yada…)
She wouldn’t have become a vampire from the Master’s attack because there was no transfer of his blood to her. For the change to happen the human must be drained to the point of death (which she wasn’t by the Master) and then drink from the vampire.
Review the S5 opener in which she meets and feeds from Dracula. He hasn’t taken enough for her to change. IIRC her senses enhance and her strength temporarily increases and she gains the ability to resist Dracula’s “gypsy trick” mesmerism. No reason to think she wouldn’t attain the same enhancements following an actual change. Plus being evil of course.
VampBuffy, aside from being totally cool, did seem to be able to take on the Ugly Man pretty easily, if that’s an indication (although I can’t remember her doing anything other than running away from him before).
I swear I’ve heard of a non-canon story from Tales of the Slayers or something like that of someone (a vampire, I’d wager!) vamping a Slayer, but I can’t remember the specifics.
I don’t think it would happen for a couple reasons. First, vampires are super-powered because they’ve got a demon where they used to have a soul. Which is exactly what gives the Slayers their power. If a vamp tried to turn a Slayer, I suspect the two demon spirits would try to destroy one another. We actually saw something similar to this in the second season episode where we learned about Giles’ sordid youth, and they force a possessing spirit out of Jenny Calender and into Angel. So, you’d either get a regular vampire with the memories of a Slayer, or a dead Slayer with funny holes in her neck.
The other reason this would never happen is that a vampire would never risk it. Every time a vampire creates a minion, he’s also creating more competition. This is why so many vampires are shlubs and morons: they were turned because their sire thought they’d be easy to control. If turning a Slayer created an uber-Slayer-vampire, the vampire who created it would be writing his own death warrant.
I think this is a good point. Even if the Slayer powers originally come from vampires, if she was fully-vamped, it’d be like getting a double dose.
With regard to vampires never risking it, I think that pepperlandgirl is right: someone like Spike (or Angelus, or Darla) would, and did (not a Slayer of course, but a powerful personality). Spike, especially, had a thing for Slayers.
I still wonder exactly where the Slayer power is located; it can’t be fully in the “soul” slot, I think, because of its demon origins (do the shamans explicitly say it is vampire power? I don’t recall that, though it would certainly make sense).
I could see Angelus doing it, just because of the amount of destruction a VampSlayer could cause. I could see Drucilla maybe doing it, because she’s so crazy. I don’t see Spike or Darla doing it at all. Spike had the opportunity, at least twice, and didn’t take it. Darla is far too calculating to take the risk, I think.
I got the impression that it’s somehow grafted on to the Slayer’s soul. Don’t know if it’s a vampire spirit, though. Don’t think they specified.
I know the books aren’t considered canon (unless they’re by Golden/Holder… ), but this is all speculation anyway, so I’ll just throw this out there: In the book Tempted Champions, Buffy meets a VampedSlayer who has the best of both worlds. Probably because it’s cooler that way.