Act 3 is a short, fast run to the boss. The level itself is straightforward, with a few downhill sections and springs. Focus on collecting as many rings as possible before the boss fight. There are usually a few ring monitors and a shield monitor available just before the boss arena.
Boss: Egg Mobile (Spike Ball Pendulum). Dr. Robotnik will appear in his Egg Mobile, which is attached to a large, spiked ball that swings like a pendulum. The arena has a flat ground. Robotnik will fly back and forth across the top, dropping the pendulum. To hit him, you need to jump and hit the Egg Mobile itself when it's vulnerable, usually when he is at the peak of his swing or just after he has dropped the pendulum. The spiked ball itself is dangerous and will damage Sonic. Hit him eight times. After each hit, he will speed up or change his pattern slightly, sometimes swinging the pendulum faster or dropping it more frequently. The key is to time your jumps carefully to avoid the pendulum and hit Robotnik when he is exposed. This boss requires good timing and quick reflexes.