An Implant Without a Source

Implant: Fit as a Fiddle exists in the game's item data, but no shop, loot table, or reward currently hands it out — and the Pal Surgery Table never asks for it. It's an unused leftover: you can't get it, and you don't need it.

How to Get Fit as a Fiddle Anyway

The passive this implant would unlock, Fit as a Fiddle (Max Stamina +25%), is one of the default options at every Pal Surgery Table — no implant needed, just 10,000 gold per surgery. The bigger stamina tiers do need items: Infinite Stamina comes from Implant: Infinite Stamina and Eternal Engine from a disposable implant. See the implants guide for how surgery works and which implants are actually obtainable.