When Jonathan Hickman's run on X-Men began it made seismic shifts with the mutants of the world, one of which was a permanent work around they'd conceived of to get around dying. The process for resurrecting mutants has already been used a number of times as characters like Cyclops, Jean Grey, Wolverine, and even Professor X have died throughout the past year and come back in brand new bodies. With the giant X-Men crossover event "X of Swords" (pronounced "Ten of Swords," like the Roman numeral and the Tarot card) now officially underway, and the first casualty already claimed, a major change to the those resurrection protocols has now been revealed
Spoilers ahead for the next chapter of X of Swords, X-Factor #4!
As revealed in X of Swords: Creation #1, Rockslide was killed while in Otherworld with the group of mutants that went to investigate. He wasn't the only mutant that didn't make it either as Rictor was revealed to have died after they returned to Krakoa through the Eternal Gate. When "The Five" went to resurrect the two mutants, Rictor managed to come back totally unscathed and returned as expected. Rockslide on the other hand, came back wrong.
When Professor X used Cerebro to "upload" the backup of Rockslide into his new body, the entire unit (and all four of the back up Cerebros) was fried and sent offline. Rockslide's body and voice began to change and mutate before they finally realized what went wrong, he didn't die on Earth, but in the Otherworld, which caused a corruption in his Cerebro back-up.
As The Five explain it to The Quiet Council, "For resurrection purposes -- Otherworld is less like a place and more like... a convergence of possibilities. What was do know is that dying their forfeits your identity, memories, experiences, physicality -- everything from this reality will be lost upon resurrection. The outcome is a gamble, but the absolute is that you will be rewritten. Every previous backup will be erased and replaced with this new amalgamation. Thus removing the possibility of a true resurrection ever again."
They continue, "Resurrecting from an Otherworld death... it creates a brand-new composite drawn out of the nearly infinite possibilities of all of the thing you ever could have potentially become. So it's someone who is you, but also someone who is....new."
In other words, Rockslide might be back but he's no longer the personality that they once knew and is an entirely different version of himself. This might not seem like a huge deal considering he's a minor X-Man as it were, but the rest of this extensive crossover hinges on a major event: ten champions from Krakoa with their swords must all travel back to Otherworld where they will engage against the ten champions of Arakko and their swords in a battle to the death.
The combatants that have been confirmed to wield the swords in the event that we know of so far (revealed by a prophecy seen in X-Factor #4) includes at least Magik, Cable, Storm, Wolverine, Gorgon, and Apocalypse, leaving four spots open. With the newly established rules of resurrection though, it's unclear who of these might perish on Otherworld and then if they will even want to be resurrected since they'll no longer be themselves. Time will tell, but it seems likely someone will be forever changed by the end of the event.
The X of Swords crossover continues on from now through November though, with the next six chapters all being released over the next two weeks. Wolverine #6, X-Force #13. and Marauders #13 will be released on October 7th, functioning as chapters 3, 4, and 5 respectively; while Hellions #5, New Mutants #13, and Cable #5 all arriving on October 14th. You can find the full checklist for the 22 part event below.