Ash comments
Load the game and allow the opening sequence to complete. Leave the game at the "Push Start" screen and Ash will eventually start to make comments.
More mushrooms
When mushrooms appear, collect them, leave the screen, then return to collect them again. Repeat this until they no longer appear.
Finding mushrooms
When you are mixing mushrooms in your inventory, you will hear a sound. When you are wandering around the same sound will indicated that a mushroom has appeared. You can also wait for the sound to play again to get another mushroom. Note: Listen for that sound when fighting the last Boss.