I was really impressed with the Genie Big Bad in the Buffy roleplaying game. It was evil and had been entrapped, but could eat souls by granting wishes, the wishes turning out bad for the one who got their wish, and eventually giving the genie more power to break free of its prison. IIRC, it started off with a bullied student who was wishing for characters of TV shows to kill his enemies, and characters from Terminator to Xena to even Captain Kirk were showing up (of course these were only quasi-real creations, like holograms that could kill, and had very little in the way of free will or leaving anything behind once killed), and later the Genie finds one of the demons or vampires escaping the Initiative and promises to help it defeat the Slayer and take over the world...that one was brilliant, and I absolutely loved the end of that adventure which really made the genie a fearful opponent as tricky as it was powerful, and after using the wishes of demonkind to free itself (at the expense of the demons making wishes), I shuddered as it offers each of the heroes a wish "in gratitude" (IIRC). I think it would've been even more fearsome than Glory, though once freed it was no longer confined the Hellmouth and seemed uninterested in hanging around.
That's all I can think of at the moment...but one element I wished the show included was a paranoia factor (like a bloody body snatcher thing), and would include say parents of the Scoobies being turned into vampires to get at them, and could even get a teacher just turned to "schedule a parent-teacher conference" which is strange but could be made to work. Even scarier, a Watcher is turned who calls Giles away to then turn him and have him lure the others into an ambush. Granted, this would be a much more horrific show, one that could make a grim Buffy from The Wish (say if her own mother, and perhaps father, were turned, as well as Giles), and make them all more cautious with no room for the charming innocence the early seasons had at times. This would work best if Jesse had been developed more as a character who was then turned later on, and it was not then conveniently forgotten after.
