Essential X-Men, Vol. 6

“Mutant” means “change,” and there was plenty of that when the Uncanny X-Men counted down to the Marvel Mutant Massacre, beginning with the trial of Magneto!
Rachel Summers became Phoenix and the Brotherhood became Freedom Force! Lady Deathstrike became a cyborg, Moonstar a Valkyrie, Colossus a killer, and Psylocke an X-Man!
And Sabretooth first set his clawed foot into the X-Universe alongside his fellow Marauders! Guest-starring the original X-Factor, Power Pack and Thor! Gods, Morlocks, talking frogs and more!
Collects Uncanny X-Men #199-213, New Mutants Special Edition #1, X-Men Annual #9, X-Factor #9-10, New Mutants #46, Thor #373-374 and Power Pack #27