X-Men: The Last Stand

X-Men: The Last Stand (2006) — A mutant "cure" is developed. Jean returns as the Phoenix, kills Cyclops and Xavier, and is stopped by Wolverine. Beast (Kelsey Grammer) debuts as a member of the US Cabinet.

A pharmaceutical company synthesises a mutant "cure" from a boy whose power suppresses other mutants, and the film's real argument is whether a cure is compassion or eradication — Rogue wants it, which the film refuses to treat as weakness. The government weaponises it into darts, and Magneto declares war.

Jean returns as the Phoenix, and the deaths are the film's other half. She disintegrates Cyclops, then Xavier when he tries to reimpose the psychic barriers he built in her mind as a child without her consent. Wolverine kills her at her own request. Days of Future Past subsequently overwrites all of it.