Quick answer: Pick up Forged Otherworldly Copper on the Puppet Cell floor, about 18 m from its bell on the Mountain of Imprisonment, or buy it from Quick Hand Zhang at his Mirage Estate hideout for 2,880 Remnant Dust.
What it does
The item card reads:
“After ten thousand hammer blows, Otherworldly Copper reveals mottled patterns across its surface. Study them with a still mind, and they resemble the paths of fists and the traces of blades, embodying the very essence of martial arts.”
“Required to upgrade Martial-type Phantom Edges from Lv. 20 to max level.”
Exotic Copper Ingot takes a Martial-type Phantom Edge to Lv. 10, and Otherworldly Copper covers Lv. 10-20. From Lv. 20 to max level, you need Forged Otherworldly Copper.
Where to find it
Beneath the hall at The Lady’s Shrine is the Puppet Cell; entry requires the Flying Guillotine.
The same floor also holds a Remnant Dust pickup worth 22,376 and Forbidden Camphor Timber.
Buying it
Quick Hand Zhang sells Forged Otherworldly Copper at his Mirage Estate hideout. Each one costs 2,880 Remnant Dust. Check the full list of materials in the upgrade guide.
