Marvel Premiere Classic Vol 21: X-Men: Proteus HC

One of the X-Men’s greatest allies must face her darkest secret when a child born of violence bends reality to his whims! The paranormal Proteus battles the X-Men in body and soul, shaking the psyches of even their strongest! But as Marvel’s mightiest mutants face one world-threatening wonder, an even worse one awaits as the stage is set for the debut of Dark Phoenix!
Collecting X-MEN #125-128, and CLASSIC X-MEN #32-33 and #36.