In Terry Pratchett's Discworld novels, elves are extradimensional inhuman monsters. Elves on the Discworld are based more on the nastier kind of fairy-folk in British and European folklore than elves as portrayed in most modern (post-Tolkien) fantasy fiction. They are not native to the Disc, but come from a "parasite universe", sometimes called Fairyland. This pocket dimension can latch onto different universes at certain times, allowing the elves (and other fae creatures such as unicorns...
