Mushroom

Mushrooms are, like their real-world counterparts, small spore-bearing fruiting bodies of fungus that Link can pickup and use during various events. The Mushroom is one of the few acquirable items that Link cannot actually use on himself; the toadstool is either given to and used by someone else, sold, or used a stepping stone to obtain some great treasure as part of a trading sequence.

As Part of Trading Sequences
In Ocarina of Time, the Mushroom is part of the Adult trading quest. Grog gives an Odd Mushroom to Link in exchange for Cojiro. The mushroom is then to be delivered to the Old Hag in Kakariko Village to be made into Odd Potion. The Odd Mushroom goes bad after three minutes (or instantly after teleporting), and cannot be delivered in such a condition. The mushroom returns again as a trading sequence item in Oracle of Seasons. Using a Megaphone, Link can wake up the slumbering Talon in a cave atop Mt. Cucco. In exchange for waking him, Talon will offer Link a Mushroom, which can in turn be given to Syrup of Sunken City in exchange for the Wooden Bird.

Used to Barter or Sell
In A Link to the Past and Link's Awakening, the Magic Mushroom or Sleepy Toadstool can be respectively found within Lost Woods and Mysterious Woods. In either game, Link can offer it to the witch in exchange for Magic Powder. In Majora's Mask, a Magic Mushroom's scent can be detected with the Mask of Scents and stored in an Empty Bottle. One can be found in the Woods of Mystery, and another can be found growing on someone's boxers in Stock Pot Inn. These can be sold to the Magic Hags' Potion Shop in Southern Swamp for 40 Rupees each, and at least one must be delivered before Blue Potions can be purchased there. Lastly, in The Minish Cap, the Wake-Up Mushroom can help Link get the Pegasus Boots. It is bought from Syrup the Witch, at the price of 80 Rupees. It is then given to Rem, the owner of the shoestore, waking him up. In return, Link will receive the Pegasus Boots. In this game, there is also elastic mushrooms that can be sucked by the Gust Jar, while Link is in Minish size, to fling across holes.

Trivia

 * In Link's Awakening, the Mushroom is one of many Mario references. When Tarin (who bears an uncanny resemblance to Mario himself, and also shares his love of mushrooms) eats one, he turns into a raccoon (although Mario himself required a different power-up item, the Super Leaf, to turn into a tanooki raccoon). Tanuki are well known for playing tricks in Japanese folklore.
 * If Young Link visits Gerudo's Fortress in Ocarina of Time (which can only be done by exploiting hacks or glitches), he can find an Odd Mushroom in the chest atop one of the buildings.
 * The Rock Mushroom, also known as Petri Fungus, is a kind of mushroom in Oracle of Seasons that is only pickable in autumn. They serve as obstacles that is blocking the way to certain areas or objects. In their pickable form they do resemble fly Amanita, but otherwise they do look like compact rocks that are shaped like mushrooms.