The roles of the characters of X fandom are swapped as much as possible. Obviously some roles are situational or personality-based rather than random enough to swap (SG-1's roles are (military) hard scientist, soft scientist, military, and alien warrior. Some could be swapped easily; others would take major rewriting of backstory and even names- Sam Carter is the former first prime of Apophis...but then what about Jacob? Why do they have American names? Etc.), but for instance I could see it going well with Buffy: Willow the Vampire Slayer! Xander the witch! Buffy the token normal person! (Jenny the Watcher! Giles the Gypsy!)