This simple sprite consists in five koopa shells that hold a prize. They will hide Mario, show their prizes, then spin fastly, and end up in a random position, so the player can choose the shell of his choice and win the prize it holds.
These koopas only end the level in a standard bonus game (levels 0 and 100, or using this patch), so make sure that you don't enter an exitless level when you put these!
The prizes by default are: Nothing, 10 coins, Flower, Feather, and 1-Up. Please read the instructions if you want to change them.