The Uncanny X-Men #256 (1963 1st series)
Acts of Vengeance: Part 1 of 3. "The Key that Breaks the Locke!" Story by Chris Claremont. Art and cover by Jim Lee and Scott Williams. A cabal made-up of some of Marvel's most dangerous villains has gathered together to pull their resources and finally destroy the heroes who oppose them. This inner circle consists of Doctor Doom, Magneto, the Kingpin, Wizard, Red Skull, the Mandarin, and a mysterious benefactor. Their plan is to surprise their enemies with foes whom they've never faced. In this issue, Iron Man's arch nemesis the Mandarin takes on a new apprentice - Lady Mandarin! The X-Men know her as Psylocke. NOTE: 1st appearance of the ninja Psylocke.