Mutant Massacre is a 1986 Marvel crossover spanning the X-Men, X-Factor, New Mutants, and Thor titles. The Marauders, mercenaries working for Mister Sinister, launch a brutal attack on the Morlocks in the tunnels beneath New York City.
The primary continuity of Marvel Comics where most titles take place. The designation was first used in The Daredevils #7 (July 1983) by Alan Moore and Alan Davis, originating from Captain Britain comics. Earth-616 serves as the home universe for core versions of Spider-Man, the X-Men, the Avengers, Fantastic Four, and virtually all mainstream Marvel characters.