The Forgotten Cutlass is a treasure introduced in Pikmin: Dimensional Breach. The real-life equivalent would be a discarded scalpel blade. It is held by the Man-at-Legs at the very bottom of the Mad Doctor's Citadel. Upon recovering the Forgotten Cutlass, the Ship will refine the metal into the Barrier Render upgrade, allowing all captains' punches to destroy obstacles, such as Dirt Walls and Spotcaps.

Notes

Olimar's Journal

    Today, we explored a cavern in the Perplexing Tropics, swarming with vicious beasts whose very anatomical structure is unnatural. The name "Mad Doctor's Citadel" immediately came to mind. In the dank depths of the cave, we fought a monstrous Man-at-Legs, who dropped this artifact. At first, I thought it was just a hunk of scrap metal, but upon closer examination, I noticed what appeared to be a handle at one end; thus, I have concluded that this treasure is a sword, one that was once used by a dread pirate lord. Hey, it appears that this region was once a sea, so the idea isn't that far-fetched."

Shacho's Sales Pitch

    An antique blade recovered from a deep cave in a long dried-up sea! Our historians say it was once the weapon of a dreaded pirate lord, or lady, as the case may be! Either way, you too can sail the seven seas searching for treasure!

Sagittarius' Journal

    We delved into a deep cave swarming with fierce robot-monster hybrids today. Yes, like something out of those old comic books I enjoyed when I was little. "Awesome" could not even describe the experience I had down in that cave; when we were fighting that abomination, the Man-at-Legs, I'd never felt so alive! Ahem, anyway, the creature dropped this hunk of metal, which dad thinks might have once been a pirate's sword. I've been trying to draw pictures of what this pirate may have looked like when they were alive, but I think I keep getting details wrong. Is their skin supposed to be purple?

Derrick's Grimoire

    This blade was likely once used by a dread pirate, who ruled the long-dried seas with an iron fist. Preliminary scans indicate that it is attuned to a spirit still haunting these lands. Here's the fun part, though: the spirit attuned to the blade is a benevolent guardian, not the pirate themselves. If I could capture the guardian spirit, perhaps all of my darkest wishes will come true... But I can't make any sense of the spirit's unique energy signature. Come to think of it, it's been a while since I've given my instruments a good cleansing...