This does not exist in Minecraft. It's just Fiction
Leether Mushrooms can grow in dark caves and shady areas. They are more readily available in Leether Swamps and Caverns /Abondoned Mineshafts/ Strongholes/. They have also been known to spawn in jungles or planted on Trees. Them alone will increase the air block it occupies by one light level.
Leether Mushrooms can be collected by hand and planted on the ground in light levels below 13 and not directly underneath the sky. They cannot be grown to be Huge and them as well as the Leether Flowers replaces the Trees. When you milk a Moogold using a bowl you can get the Leether Soup or you can just craft it.
They can be crafted to make Leether Soup by placing a Gold Nugget and Mushroom Stew.
- They are the golden version of the Brown Mushroom.