Go to first zone,Angel Island with any character,get on a swingy thing,press right 3 times,left 3 times,and up 3 times(you will hear a ring sound).then press enter then a and will go back to title if done right.scroll down past comp. then there is sound test which is a level select.if you want debug mode , do the code for level select,then go to mushroom hill act 1.do the same thing that you did on swingy thing on a pulley thing(youll hear a chime) go to title. go to level select and to start with debug mode press a and enter @ the same time to play with debug mode(can do with any level except doomsday zone.be careful though.it sometimes glitches and switches to sonic & knux.and the #s stand for what characters. press d to switch characters.these are the things for the characters:
00=Sonic+"Tails",01=Sonic,02="Tails",03=Knuckles
HOPE IT WORKS!!!IT DOES FOR ME!!!
-DDXHAWK