The love of crossover fanfic is the root of all evil
As reward for getting on with tidying the house, to make it saleable, I decided that I really wanted to rewatch Buffy, and so bought a complete box set. 
minion_of_tevildo and I have thus been watching it in our breaks, and are currently about halfway through season three. We've discussed a few crossover ideas (notably involving what various canons would make of Spike) over the last few days, but this evening's idea came suddenly and with the force of a lightning bolt:
Bodyswap: Cordelia Chase / Cordelia, Countess Vorkosigan
The most likely suspect is, naturally, Ethan Rayne, looking to cause mischief but not particularly interested in getting anyone killed. Swapping a (from his perspective) minor member of Buffy's support team for a random other person with the same name should be fun, right? I'm not quite sure that even Cordelia V. is going to be able to actually turn him into a good person, but I do think he's fairly rapidly going to wind up more alarmed by her than he is by Giles. While tracking him down, of course, she's going to give the Scooby Gang the Betan sex-ed treatment for their idiotic love-lives, permanently readjusting a number of heads (and extracting a few from colons somewhat prematurely, from the series point of view). She's not going to have much sympathy for the Council's bullsh*t, either; post-"Helpless", Giles is going to find himself with an unexpectedly potent ally, and Wesley is in for a torrent of pain when he arrives. She might even be able to rescue Faith from herself, if she arrives early enough.
On the other end, Cordelia C, dropped into the Vorkosigan family, is going to have a harder time of it. Even if she works out what's happened fast enough (which she should do; she's smart[1]), she's not going to fool any of the other Cordelia's family or friends for an instant. They're going to work out that she's an imposter equally fast, and while (post-Mark, at any rate), they'll be open to the idea that the imposter is relatively innocent, the idea that she has no idea where she is or what's going on is unlikely to be accepted. Once she gets over the initial panic, and they all get pointed in the right direction, things will be alright (for her; Ethan is in a world of trouble at this point[2]), but before that, Cordy will have a very bad time. [ETA: for bonus points, there needs to be some unavoidable social situation in which CC has to pretend to be CV, under the supervision of Lady Alys. Because seeing CC come up against that immovable object on the subjects of fashion and etiquette...] There could also be some serious political strain. Depending on the timing, Cetaganda or one of the Jacksonian houses could plausibly be blamed for the switch, with everyone on Barrayar simultaneously trying to point fingers and keep it quiet that anything's happened. Then, of course, they don't believe in magic (or, presumably, have any local expertise), so they're probably just going to have to wait for their Cordelia to get everything in line back in Buffyland and get the spell reversed.
[1] She's going to get some very interesting life-lessons about (a) being overly self-interested and (b) pretending to be stupid.
[2] Seriously, Aral's response to someone kidnapping his wife as a joke? Miles and Gregor will merely be homicidal; Aral will be much, much scarier.
minion_of_tevildo and I have thus been watching it in our breaks, and are currently about halfway through season three. We've discussed a few crossover ideas (notably involving what various canons would make of Spike) over the last few days, but this evening's idea came suddenly and with the force of a lightning bolt:
Bodyswap: Cordelia Chase / Cordelia, Countess Vorkosigan
The most likely suspect is, naturally, Ethan Rayne, looking to cause mischief but not particularly interested in getting anyone killed. Swapping a (from his perspective) minor member of Buffy's support team for a random other person with the same name should be fun, right? I'm not quite sure that even Cordelia V. is going to be able to actually turn him into a good person, but I do think he's fairly rapidly going to wind up more alarmed by her than he is by Giles. While tracking him down, of course, she's going to give the Scooby Gang the Betan sex-ed treatment for their idiotic love-lives, permanently readjusting a number of heads (and extracting a few from colons somewhat prematurely, from the series point of view). She's not going to have much sympathy for the Council's bullsh*t, either; post-"Helpless", Giles is going to find himself with an unexpectedly potent ally, and Wesley is in for a torrent of pain when he arrives. She might even be able to rescue Faith from herself, if she arrives early enough.
On the other end, Cordelia C, dropped into the Vorkosigan family, is going to have a harder time of it. Even if she works out what's happened fast enough (which she should do; she's smart[1]), she's not going to fool any of the other Cordelia's family or friends for an instant. They're going to work out that she's an imposter equally fast, and while (post-Mark, at any rate), they'll be open to the idea that the imposter is relatively innocent, the idea that she has no idea where she is or what's going on is unlikely to be accepted. Once she gets over the initial panic, and they all get pointed in the right direction, things will be alright (for her; Ethan is in a world of trouble at this point[2]), but before that, Cordy will have a very bad time. [ETA: for bonus points, there needs to be some unavoidable social situation in which CC has to pretend to be CV, under the supervision of Lady Alys. Because seeing CC come up against that immovable object on the subjects of fashion and etiquette...] There could also be some serious political strain. Depending on the timing, Cetaganda or one of the Jacksonian houses could plausibly be blamed for the switch, with everyone on Barrayar simultaneously trying to point fingers and keep it quiet that anything's happened. Then, of course, they don't believe in magic (or, presumably, have any local expertise), so they're probably just going to have to wait for their Cordelia to get everything in line back in Buffyland and get the spell reversed.
[1] She's going to get some very interesting life-lessons about (a) being overly self-interested and (b) pretending to be stupid.
[2] Seriously, Aral's response to someone kidnapping his wife as a joke? Miles and Gregor will merely be homicidal; Aral will be much, much scarier.