In New Super Mario Bros. Wii, there are various mushroom houses that are on the map to get items from. You can force extra ones to appear though by saving Toad from a level.
When you see a level with a toad in it, you will always gain a mushroom house after you save him, but which one you get is determined by the last digit of the time left on the clock.
Gold Mushroom House: Hit the flag with Toad in hand when the last digit is a 7, 8, or 9
Green Mushroom House: Hit the flag with Toad in hand when the last digit is a 0, 1, 2, or 3
Red Mushroom House: Hit the flag with Toad in hand when the last digit is a 4, 5, or 6
