When your total earnings reach 25,000g Demetrius will come by and tell you he has been doing research. He'll then give you the options if you want bats to leave fruits in your cave or to have mushrooms randomly grow in your cave.
Certain types of mushrooms will randomly grow, there are a total of six plots for them to grow in. The four out of five mushrooms that grow are required to create the Life Elixir. This is the best way to craft the elixir as often as possible (though mostly; Common Mushrooms, Morels, and Chanterelles, are most common) and a great option for those who love to go into The Mines. Especially since most mushrooms are quite rare.
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Name
Description
Found
Profits
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Common Mushroom
A tasty mushroom with a fruity smell and slightly peppery flavor.