Choose Sonic 3. Enable the "Level Select" code. At the level select screen, choose Special Stage 1 or 2. At the "Get blue spheres" screen, press Enter. If you start as Sonic, hit the Red spheres. The Spinning star should be red. Press Alt+R to restart the game. Choose "Sound Test". Choose a zone and act (except the Sonic & Knuckles zones). When it starts, you will be Knuckles!!!! You cannot beat the game or fight robotnik where Knuckles usually fights in Launch Base Zone Act 2.