"Mutant Massacre" was a 1986 Marvel Comics crossover storyline. It primarily involved the superhero teams the X-Men and X-Factor. The solo hero Thor, the New Mutants, Power Pack and Daredevil crossed over for an issue each in their own comic books. The crossover was a surprise success, yielding sales boosts to the mutant-based books and prompting Marvel Comics' long-running policy of holding such mutant crossovers annually.