In sonic 3 and knuckles (one of the hidden games) when you become hyper sonic and complete the game (same with knuckles) and the ending roles press A,B,X,B,left,left,up,up,down,start and load the save data of which you had just completed. the screen will turn black for a while and you will see the master emerald. jump on it to become mega sonic/knuckles. walk through a portal to go to the first level