Reach the end of Classic mode, and choose the black path on the 5.1 intensity or higher. After doing enough damage while fighting both Master Hand and Crazy Hand, Crazy Hand will leave and Master Hand will turn into Master Core. Master Core can assume many forms, depending on the difficulty. His "Sapien" form appears when the intensity is set to 7.5 or higher. His "Scorpion" form appears when the intensity is set between 6.0 and 7.4. When the intensity is set between 5.1 to 5.9, Master Core will be in "Sabres", "Simulacrum", or "Source" forms. After defeating all forms of the Master Core, its real form can be fought. Note: You are forced to fight Master Core on the 8.0 intensity and higher. In the Japanese version, you are forced to fight Master Core at on the 9.0 intensity.