In New Super Mario Bros. Wii, there is a way to make all mushroom houses stay forever, but it is very tough.
You have to collect every star coin in the game (231 in all from worlds 1 through 9), finding all of the secret exits from levels, using all warp cannons, and using all static mushroom houses.
Once this is done you’ll get a message saying that everything has been cleared, and all mushroom houses will appear on the maps again, and won’t disappear when you use them.
