Mushrooms are your primary source of health restoration in Super Mario Bros. 2. When collected, a Mushroom will restore one heart to your health meter. They are often found by throwing a Potion in a specific location to create a Sub-Space door, where the Mushroom will appear. Sometimes, they can also be found by pulling up certain vegetables. Always prioritize collecting Mushrooms, especially if your health is low, as they are vital for survival against tougher enemies and bosses. Knowing the locations of hidden Mushrooms can significantly extend your playthrough.
