To fight the secret boss "Master Core", you must play Classic mode and reach the final boss of Classic Mode on intensity 6.0 or higher, as well as choose the black path. In the fight against Master Hand and Crazy Hand, after dealing a certain amount of damage against either hand, the hands will disappear from battle, and Master Core will take their place. If you play on intensity 8.0 or higher, Master Core will have an additional form.