WARNING: The following contains major spoilers for Way of X #2 by Si Spurrier, Bob Quinn, Java Tartaglia, VC's Clayton Cowles and Tom Muller, on sale now.
In the course of their nearly sixty-year history, things have never looked brighter for the X-Men. The Hellfire Gala is on the horizon, Krakoa is flourishing as a nation and their people can feel truly safe for what might be the first time ever. Of course, that doesn't mean that they still don't have grave concerns to attend to. While the children of the mutant nation tell campfire ghost stories of the Patchwork Man, Legion and Nightcrawler discuss just how dangerous this boogieman really is. Legion knows exactly who the Patchwork Man is, and he knows that Onslaught has already returned.
Kurt has been hearing all about the Patchwork Man as he is the one subject that every mutant on Krakoa seems to have something to say about. Even Legion, after having his life ended by Nightcrawler so that he might be resurrected, is concerned with the seemingly ethereal children's story come to life. After the two mutants get a moment to themselves, Kurt asks Legion point-blank if he knows who the Patchwork Man is, and of course, he does. He doesn't want the news getting out, especially not to Xavier or Magneto, but the Patchwork Man is none other than Onslaught, and his return foretells nothing but death and destruction for the mutants of Krakoa.
The psychic entity known as Onslaught was born of the merged psyches of Professor Charles Xavier and Magneto after the latter drove the Professor to his breaking point. After watching Magneto rip the adamantium free from Wolverine's skeleton in a grotesque display of cruelty, Xavier launched a crippling psychic assault on his old rival, leaving Magneto completely catatonic. While Xavier had taken his revenge, his mind had also been infected by Magneto's worst fears and hatreds, and as those emotions festered within Xavier's incomprehensibly powerful mind, Onslaught was born. The villain proved to be even more unstoppable than the Juggernaut as seen in 1995's Uncanny X-Men #322, when an unknown assailant left the Juggernaut screaming for help once he awoke from having the Crimson Gem of Cyttorak torn from his body. When Onslaught finally revealed himself in 1996's X-Man #15 by John Ostrander, Terry Kananagh and Steve Skroce, he led a campaign of terror that nearly killed the X-Men, Fantastic Four and Avengers had it not been for the subconscious intervention of Franklin Richards' reality-warping powers. This event led to the first Heroes Reborn universe following the apparent destruction of Onslaught, but such a powerful being does not die a single time. Since then, Onslaught has been trapped in the Negative Zone, again defeated by Franklin Richards. Though he has unsuccessfully attempted to escape in the past, it looks like Onslaught has finally found a way home.
Much like Legion himself, Onslaught is one mutant that Professor Xavier, and presumably everyone else, would rather not see resurrected. That being said, Legion was able to implant his own consciousness into his new body even without the help of Xavier or Cerebro, so it is safe to assume that Onslaught would be capable of very similar feats. Worse than Onslaught alone, however, is the evidence that points to him having been weaponized against Krakoa in the hopes that his influence would push mutantkind into destroying themselves. As unlikely as that is, the presence of the Patchwork Man has already proven enough to disrupt the daily life of Krakoans in some truly unsettling ways, and if it is indeed Onslaught behind that mask, then Legion alone might not even be enough to stop him.