The prosthetic tools are nothing more than real secondary weapons that, once found, can be equipped in our mechanical arm through the wise work of the Sculptor at the Temple in Ruin. In the game there will be ten prosthetic tools, and finding them all will unlock the silver trophy "All prosthetic tools".
Prostetic Tool#3 - Flame Barrel (Flame Vent): Summer Path
Where to find it: to unlock the region called Hirata Estate you will need to talk to an elderly woman, who you will find in a destroyed house on the outskirts of Ashina, located between the areas of "Outskirts Wall - Gate Path" and "Outskirts Wall - Stairway". The character in question will give you a little bell, which you can use on the altar where the sculptor is located (Temple in Ruin).
After the idol called "Summer Path", jump through the walls on the right side until you reach a large area with an archer on a roof and many enemies around a bonfire. Inside the fire there is this tool, very difficult to see. To pick it up, basically, you almost have to get inside the camp fire. The sculptor will transform this object into the prosthetic instrument called "Flame Vent".
Prostetic Tool # 4 - Shinobi Axe of the Monkey (Loaded Axe): Summer Path
Where to find it: this tool is very close to the place where you found the previous one. From the bonfire where we took the Flame Barrel, you will have to take the path above (the one linked to the game plot). You will find a dying soldier leaning against a wall on the right side, who will tell you about an axe.
After talking to him, go left and enter the next courtyard where you will find two enemies next to a small green area (you will recognize them because you can eavesdrop on their conversation). Kill them and open the little garden house they were watching. The tool in question will be located in this area. The Sculptor will transform the Shinobi Ax into the prosthetic tool
Prostetic tool #5 - Mist Raven's Feathers (Mist Raven): Bamboo Thicket Slope
Where to find him: after killing the miniboss "Shinobi Hunter Enshin of Misen", you will reach the idol called Bamboo Thicket Slope. Follow the path immediately after this idol, until you reach a small series of stairs and then cling to the tree trunk on the left. Then jump in the water and swim against the current until you reach the end. On the right side you can grab a branch of a tree and find a bright object to collect (practically at the end of the river).
To the right of this object there is a bamboo door / barricade. Hit it to destroy it, thus revealing the path that will lead to a cave. Climb the cave wall until you reach a hidden temple on top of a mountain. A powerful ninja will appear in this area, but for now you can ignore him. Just open the temple door and inside you will find this tool which the Sculptor will transform into the prosthetic instrument called "Raven Mist".
Prostetic Tool#6 - Gyoubu's Broken Horn (Loaded Spear): Ashina Castle
Where to find it: from the first idol you will find in this region (called "Ashina Castle"), jump from the bridge on the left and cling to the branch of the tree. Here you can eavesdrop on two enemies standing on a bridge. Kill them and they will drop the Gatehouse Key. From the same bridge where you confronted them, go down the right side until you reach the idol called "Ashina Reservoir".
Remember that moment in the prologue when we were shown how to walk hidden in the tall grass? Well, we will find ourselves visiting that very area, and that is where the Gatehouse will be. The only difference is that, this time, there will be a lot of riflemen and two enemies armed with big hammers patrolling the area. Open the gatehouse with the key and, inside, there will be a large treasure chest containing this tool, which the sculptor will transform into the "Loaded Spear".
Prosthetic Tool #7 - Upper Tower - Antechamber
Where to find it: from the first idol in Ashina Castle, you'll have to jump over the rooftops on the right side and follow the smoke signals coming out of them, until you reach the big tower in the middle of the map (it's the tallest building, easy to see). When you enter the tower through the rooftops, you will find the Anticamera's idol. Go to the room where some samurai in blue robes patrol the area; jump off the tower from this point. At the bottom there will be four enemies and a treasure chest in a side room. Inside this trunk you will find the prosthetic tool you are looking for.
Prosthetic Tool #8 - Iron Fortress (Loaded Umbrella): Old Grave
Where to find it: from the idol of the Old Tomb, jump on the left side of a building with a broken roof. Go through the hole in the roof and, in this building, you will find a hidden merchant. This character will sell you the prosthetic tool "Iron Fortress" for 1600 Sen. Take it to the sculptor, who will turn it into the "Loaded Umbrella".
Prostetic Tool #9 - Large Fan (Divine Abduction): Gun Fort
Where to find him: just after the third Sunken Valley idol, called "Gun Fort", you will enter a room where the boss fight will take place. After killing this enemy, you will find the object you are looking for in this very room. The Sculptor will transform what you have collected into the prosthetic tool "Divine Abduction".
Prostetic Tool #10 - Slender Finger Whistle: Bodhisattva Valley
Where to find it: this will be obtained automatically immediately after eliminating the main boss Guardian Ape. This is the last boss in this area, and you will have to deal with it for the continuation of the main plot. The Sculptor will transform the object you have collected into the prosthetic tool called "Finger Whistle".