In Stardust Speedway Zone Act 3 you will race against Metal Sonic. Beat him without getting hit by him or any spikes and the achievement is yours. It will pop up as soon as the door closes at the end. A few tips:
• Metal Sonic cannot harm you unless he is doing an attack, so you can run right past him without having to jump over him.
• If you get too far ahead of Metal Sonic he will use his Maximum Overdrive Attack which will give him a yellow aura around himself as he crashes through spikes trying to catch up to you.
• Sometimes when you are close to him Metal Sonic will activate his Ring Spark Field. It’s best to just make sure Metal Sonic is nowhere near you all the time.
• At points in the race there will be paths above you that are safe for you to travel on.
• Don’t get too far behind in the race as Eggman (Or Robotnik, your choice) has an instant death laser and is constantly following the both of you. NOTE: If you miss this achievement during your regular game you can get it in Time Attack Mode.