I was just reading the Doctor Who novel Human Nature, now available on-line, and in the notes, the author (Paul Cornell) reveals he was considering having the villains be “all thirteen incarnations of one evil Time Lord, who went about in a big gang.” http://www.bbc.co.uk/cult/doctorwho/ebooks/human_nature/intro/page3.shtml
What a freaking brilliant idea. Sure, it makes no sense to those who have never seen the program, but to me, wow. A groups of troublemakers, walking down a road, kicking cats, and other forms of villainy, and all bickering with one another, despite the fact they are all actually the same person.
Anyway, any other idea you have heard proposed by authors that have never been used?