"Mutant Massacre" was a major Marvel Comics crossover storyline, which took place during late 1986. It primarily involved the superhero teams the X-Men and X-Factor and 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's long-running policy of holding such mutant crossovers annually.

The mysterious Marauders attack a mutant named Tommy and her Hellfire Club boyfriend in Los Angeles for the purpose of following her back to New York and finding the location of the underground mutant community known as the Morlocks. The Marauders kill Tommy and hundreds of Morlocks before the X-Men and X-Factor teams arrive separately and fight them, avoiding the total slaughter of the Morlocks. The two teams however do not meet during the battle and suffer crippling losses: X-Factor's Angel is crucified by the Marauders while the X-Men's Colossus, Shadowcat, and Nightcrawler are all severely wounded. X-Factor's casualties are less due to the arrival of Power Pack and Thor, who help save the horribly wounded Angel and the rest of X-Factor from suffering any additional harm.

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