Amber is a reference to a series of fantasy novels by Roger Zelazny, beginning in 1970 with “Nine Princes in Amber,” which served as the foundation of the game. Mush is an acronym for the form of the game, known winkingly as a “multi-user simulated hallucination.” In the Amber world — shut down since 2009 but fondly remembered on tribute Web sites — participants created characters and developed scenarios, constructing the action as they went along in a kind of pick-up game of make-believe. With no graphics, Amber was a world made of words. For aspiring writers, as Mr. Butcher was back then, that was very enticing.