In Sekiro, finding the various Prosthetic Tools makes all of your fights easier by adding tools to your arsenal. You’ll pick up the first — the Shuriken Wheel — just before your fight against General Naomori Kawarada. The next Prosthetic Tool you’re after is called Robert’s Firecracker — which the Sculptor will turn into the Shinobi Firecracker.
This isn’t one you can find, though. Instead, you’ll have to purchase it from a Memorial Mob vendor. Happily, there’s one early in the game (before you even reach the Chained Ogre) that you probably missed (we sure did in our first games).
Ashina Outskirts Memorial Mob
You’re looking for the house where you speak to the old woman — Inosuke Nogami’s Mother — who gives you the Young Lord’s Bell Charm. It’s about halfway between the Ashina Outskirts > Ashina Outskirts and the Ashina Outskirts > Outskirts Wall - Gate Path Sculptor’s Idols — it’s not too far past where you fought General Naomori Kawarada.
From that house, head downhill a little more, past Inosuke Nogami. Just before you reach the gate — where the guard with the mortar cannon will spot you, turn to the left and grapple up. At the ledge, turn left again and grapple up some more. Follow the path you land on a little ways until you can grapple up one more time. If you’re quick and watch where you’re headed, you can hit all three grapple points without touching the ground like we did in the video above.
At the top, you’ll meet the Memorial Mob. He’ll sell you an item called Robert’s Firecrackers for 500 sen. (If you need money, you’ll find three Light Coin Purses in the hidden room under the old woman — just watch out for the two roosters guarding it.) Take the Firecrackers back to the Sculptor, and he’ll turn it into the Shinobi Firecracker. It’s especially useful against an upcoming boss, Gyoubu Oniwa.