Where To Find The Pangzhen Backstreet Courtyard Key In Phantom Blade Zero

In Phantom Blade Zero, the Pangzhen Backstreet Courtyard Key is found in the Mountain of Imprisonment, in the area on the way to the Shrine Outer Gate where the Agonized Ironmask and the Female Puppet Bai Xue appear. After completing Hero's Lament/Moji's Relic, the Agonized Ironmask offers the Ledger of Atonement side quest; handing over a book from the caves and defeating him drops the key. Bai Xue then asks you to bring the Bloodstained Necklace to her real body, which the key lets you reach by opening the locked gate near Old Man Gen's house in Pangzhen Green Serpent House.