Spoilers below for X of Swords!
The X-Men just emerged from a deadly war and not all of them survived. X of Swords was the first real test for the mutants' new nation, Krakoa, as they fought a clan of mutant warriors who rank as strong or stronger than Apocalypse himself. The tournament mixed contests of strength, wits, and luck with old-fashioned fights to the death. Now that X of Swords is over, here's a list of the casualties.
Rockslide: The First Victim
At first, the prospect of a fight to the death seemed low-stakes, since the X-Men have learned how to resurrect themselves via cloning. But when the mutants of Arakko declared war, they kicked it off by killing the young X-Men hero Rockslide. The X-Men found out that dying in Arakko's realm, Otherworld, made it impossible to bring them back. Rockslide showed mutants that dying in X of Swords mattered, as much as comic book death can matter.
Summoner: Slain By Wolverine
Rockslide's murderer was Summoner, an Arakko mutant who seemed to be a friend to the X-Men. The invulnerable mutant was actually a traitor who belonged to the Vile School, an Arakko cult that summoned demons and created mutant-demon hybrids. Wolverine avenged his student when the pair were matched up in a fight to the death and Logan threw his katana through Summoner's eye.
Nanny: Destroyed By The Vile School
The Hellions are the X-Men's new Suicide Squad, a collection of troubled heroes and dangerous villains who perform suicide missions. One of the Hellions is Nanny, an egg-shaped cyborg who acts as the doting, controlling mother to an emotionally stunted super-soldier named Orphan-Maker. The Hellions tried to infiltrate Arakko, but a group of Vile School mutants called the Locus Vile obliterated them, starting by blasting Nanny to bits.
Captain Britain: Shattered To Save The Multiverse
X of Swords seemed like a straightforward fighting tournament until the first battle between Krakoa and Arakko. Captain Britain, aka Betsy Braddock, formerly Psylocke, stepped up to the arena to duel Isca the Unbeaten, whose mutant power is that she can never lose. Her power went unquestioned when the battle began and Captain Britain instantly disintegrated into shards. This turned out to be part of a scheme by the tournament organizer, Saturnyne, who assembled the shards into a magic circle. In the demon war of X of Swords' finale, that magic circle summoned a new Captain Britain Corps and saved the day.
Gorgon: Died To Even The Score
The X of Swords tournament was practically made for Gorgon, a swordmaster who can turn enemies to stone with his gaze. The former Hydra leader was matched up against The White Sword, a healer mutant who lets his army of a hundred resurrected warriors fight for him. With his god-killer katanas Grasscutter and Godkiller, Gorgon cleaved through waves of immortal enemies until the horde finally brought him down. Saturnyne revealed that every kill Gorgon made counted as a point scored, giving the heroes a fighting chance.
Apocalypse: Not Dead, But Gone
In the final battle, Apocalypse made good on his aim to save Arakko rather than destroy it. He defeated his wife and took her place as Arakko's leader by right of victory, which he used to surrender. The pair reconciled and left to rule Arakko together. Apocalypse survived, but he's off the team and his story is over for now. For the X-Men, that consequence can last longer than death.