In Sekiro Shadows Die Twice there is a hidden Shop Merchant, if you find him you also unlock the following achievement / trophy:
Encountered the Memorial Mob
More solutions and tips on the game can be found on our overview page for Sekiro: Shadows The Twice.
Find the Memorial Mob
You can unlock this trophy early in the game once you reach the Ashina Outskirts. Where you have defeated "General Naomori Kawarada", then follow the path to the left. There is a big mountain on the left side of the area. With the grgrapple tool you can reach the top. On the mountain you will find a tent with the merchant.