During the Mutant Massacre, Colossus became heavily involved in the X-Men's efforts to save the Morlocks from the Marauders. When Kitty was severely injured by Harpoon, Peter gave in to his rage and snapped Riptide's neck. He eventually passed out from previous wounds inflicted by Riptide. Magneto, with the aid of Shadowcat, used his powers to heal Peter's armored form, but the process left him paralyzed. He was sent to Muir Island to recuperate, along with Nightcrawler, Shadowcat, and the surviving Morlocks.