Certain treasure that you find can be used to enhance your space suit, lets you discover new areas, or use sprays to battle enemies. Here is a full list of those special items, where to find them, what they do, and which boss you need to defeat to acquire it.

Unlockable	How to unlock
Anti-Electrifier (Makes Your Suit Immune to Electricity)	Defeat the Giant Breadbug on Floor 6 of the Glutton's Kitchen.
Mega Tweeter (Increases the Range of Your Whistle)	Defeat the Ranging Bloyster on Floor 7 of the Shower Room.
Metal Suit Z (Increases Your Suit's Durability)	Defeat the Pileated Snagret on Floor 7 of the Snagret Hole.
Napsack (Take a Nap by Holding C, the Pikmin Will Carry You Back to Your Base)	Defeat the Burrowing Snagret on Floor 5 of the White Flower Garden.
Pluckaphone (Plucks Pikmin in the Ground by Whistling)	Defeat the Waterwraith on Floor 5 of the Submerged Castle.
Rocket Fist (Increases Punching Power)	Defeat the Mamuta Holding It on Floor 5 of the Frontier Cavern.
Rush Boots (Immunity to Blowhog's Wind and Increases Running Speed)	Defeat the Empress Bulblax on Floor 8 of the Frontier Cavern.
Scorch Guard (Makes Your Suit Immune to Fire)	Defeat the Emperor Bulblax on Floor 7 of the Bulblax Kingdom.
Solar System (Lights up Caves)	Defeat the Man-At-Legs on Floor 9 of the Subterranean Complex.
Sphere Chart (Unlocks the Awakening Wood)	Take it Back to the Research Pod on Floor 2 of the Emergence Cave.
Survey Chart (Unlocks the Perplexing Pool)	Take it Back to The Ship at the Awakening Wood.
The Key (Unlocks Challenge Mode)	Defeat Beady Long Legs on Floor 5 of the Citadel of Spiders.
Treasure Gauge (Beeps When You're Near Treasure)	Defeat the Empress Bulblax on Floor 5 of the Hole Of Beasts.
Ultra Bitter Spray (Increases Pikmin Speed and Power)	Found Scattered Above Ground At the Awakening Wood, Perplexing Pool, and Wistful Wild, Also Found n Eggs.
Ultra Spicy Spray (Freezes Enemies by Turning Them to Stone)	Found Scattered Above Ground At the Awakening Wood, Perplexing Pool, and Wistful Wild, Also Found n Eggs.