The Longest Fanfiction is about Super Smash Bros
One source states, "Writers of fan fiction have the wildest imaginations and often put our favourite characters into bizarre and fantastic situations. Some examples of fan fiction are just plain bad, while others attempt to outdo the universe from which they are inspired. The most recognized homage to Smash Bros. falls into the latter category and it harbours a truly impressive merit: it is the longest work of fan fiction ever written. Clocking in at 3.5 million words (and counting), is longer than the entire Lord Of The Rings trilogy, trumps the Bible, and is six times longer than the Infinite Jest. The story revolves around the relationships between Smash Bros. characters as they journey to the real world in an attempt to stop the Subspace Army (or something like that). Venture forth with an open mind and a whole lot of spare time"(Reid).
