Players seeking the Pangzhen Backstreet Courtyard Key in Phantom Blade Zero may find its location tied to specific quest progression and NPC interactions. The key is ultimately found in the Mountain of Imprisonment, within an area encountered en route to the Shrine Outer Gate. This particular area features two non-player characters: the Agonized Ironmask and a Female Puppet.
Initially, interacting with these NPCs may yield no immediate results, even after completing the primary quest objectives in the region. However, progress in the Hero's Lament/Moji's Relic questline triggers new dialogue options with the Agonized Ironmask. This leads to a short side quest, the Ledger of Atonement, which involves delivering a book found in nearby caves to the NPC. Following this, players will engage in combat with the Ironmask, who will drop a Sha-Chi Amber Fragment and the Pangzhen Backstreet Courtyard Key upon defeat.
With the key in hand, players can then progress Bai Xue's quest, initiated by the Female Puppet following the Agonized Ironmask's demise. Bai Xue tasks the player with delivering a Bloodstained Necklace to her true body. Returning to the Pangzhen Green Serpent House, players can use the key to open a locked gate near Old Man Gen's residence. Beyond this gate, players must ascend the walls to reach a rooftop, granting access to Bai Xue's home.
Upon entering Bai Xue's home, the Bloodstained Necklace should be placed near her real body, which causes a Memory Flower to spawn. Another Memory Flower petal is located in the yard outside. Players can then interact with the large tree trunk in the yard to obtain the Snow & Blood accessory. This item enhances damage against bleeding enemies and increases all enemies' susceptibility to bleeding damage by 20%.