It doesn't truly fit your criteria either, but 'Clocks of the Long Now' certainly sets Giles up as a Big Bad.

I've also seen a story where Spike and Buffy time-travel back to the 70's and encounter Ethan and Ripper. Not quite Giles as *the* Big Bad either, but it provides a glimpse of a somewhat out of control Giles. I can't remember who wrote it or what it was called though.

I was actually thinking about Giles, his push for independence, and leaving in S6, and really, Tony had other places to be that season. That's it. Otherwise, him leaving - especially the first time, before they raise Buffy from the dead - makes zero sense. *Giles* would leave the Hellmouth unprotected and Dawn without financial security? Uh... NO. That was just to prepare us all so it wasn't so surprising when he left again. The entire set-up to Buffy's big crappy year is poorly done. I'm really supposed to believe that nobody was contributing financially? Hello, what would have happened if they hadn't managed to bring Buffy back? If it had been RL rather than plot contrivance (ignoring that there's no raising the dead in RL :)), the financial stuff would have been taken care of, not left to pile up. There's no way ANY of those normally responsible adults would have left Dawn in such dire straights. I can't hate the Scoobies for their giant, writer-caused, OOC behaviour when it comes to the financial stuff that is, for some strange reason, all Buffy's responsibility.