Olivia Munn's Psylocke was introduced in X-Men: Apocalypse as Caliban's bodyguard, but when Apocalypse came to her employer in search of mutants to join his cause, the ancient Egyptian mutant recruited Psylocke and turned her into one of his Four Horsemen. Psylocke later fought Beast during the movie's climactic battle, and after Apocalypse was destroyed through the combined efforts of Jean Grey, Cyclops and Magneto, she left the area without saying a word. If Psylocke does indeed appear in X-Men: Dark Phoenix, it will be interesting to see whether she remains an X-Men adversary or if she'll follow after her fellow Horseman Storm and decide to join the team. Approximately a decade will have passed in the events of X-Men: Apocalypse, so surely that would be enough time for her to have possibly walked away from her old life in favor of using her energy abilities for good.