Mushrooms do best when they can breathe. Leaving them in a paper bag on an open shelf in your refrigerator will ensure longest shelf life. Oyster mushrooms typically last 5 days before they start to brown and wilt on the edges. As long as your mushrooms aren't slimy and don't have an off smell, a little browning and drying won't affect their taste significantly. Lion's Mane, Chestnut, King (including Black Pearl) Oysters can last 7 days or more properly refrigerated. You can also cook them in a dry pan on medium low heat to just cook them through, cool them and refrigerate before they go bad to extend shelf life a little longer. You can also freeze up to a couple months after this process as well.