I know the kind of mutants you’re looking for. And I know where to find them.
Psylocke is a recurring antagonist of the X-Men film series, serving as a minor antagonist in X-Men: The Last Stand and a supporting antagonist in X-Men: Apocalypse. In the original timeline, she was a member of Callisto's Omega Gang, a group of mutant outcasts based in an underground network in the United States. In the revised timeline, she's the second Four Horsemen of The Apocalypse.
When the mutant cure was created, Psylocke and the Omegas protested, saying that there was nothing wrong with mutants and therefore, nothing to cure. Callisto decided to join Magneto's Brotherhood of Mutants. The rest of her group, which included Psylocke, Quill, and Arclight, followed, and became leading members of the Brotherhood.
Psylocke and the Omegas fought in the battle on Alcatraz Island, where she, Quill, and Arclight entered Worthington Labs while the rest of the mutants fought outside. Psylocke captured Warren Worthington, and attempted to kill him by throwing him off the balcony, but his son saved him before he could hit the ground. When Phoenix began to destroy Worthington Labs with her disintegration wave, Psylocke tried to escape the building but was killed.
For an unknown length of time, Psylocke was the assistant of Caliban, a mutant who could locate other mutants. The two would eventually get approached by Apocalypse and Storm, who were in search of new members to recruit to their cause. However, after the two threatened Caliban, Psylocke held both mutants at knifepoint with her blades. Amused, Apocalypse convinced her to join them before giving the mutant more power and a new uniform. Psylocke would then accompany the two as they recruited Angel and Magneto. Upon capturing Xavier and seizing control of Cairo, Apocalypse prepares to transfer his consciousness into the mutant while ordering his followers to protect him. When a group of mutants led by Mystique arrive aboard a jet, Psylocke gets into a fight with Beast which ultimately culminates in her getting thrown onto a rooftop. Later, as the mutants rescue Xavier and attempt to flee, Angel and Psylocke manage to get onto the jet as it takes off. However, thanks to Nightcrawler's ability to teleport, the heroes escape, leaving the two mutants behind on an aircraft heading towards the ground. Although Psylocke manages to get blown off, Angel is unable to escape as the jet crashes and explodes. Following Apocalypse's demise at the hands of Jean Grey, Cyclops, and Magneto, Psylocke leaves the area.
Munn was initially offered the role of Vanessa Carysle in the film Deadpool, but she was disinterested in playing the role of the girlfriend. However, Kinberg wanted her to have a role in the X-Men Cinematic Universe so much that he and director Bryan Singer approached her with the role of Psylocke a few weeks later.