You must defeat 15 rivals to reach the top. Each rival requires you to complete a set of challenges—such as Circuit races and Time Trials—before you can face them in a 1-on-1 boss event.
In this version, nitrous acts like a "jet engine" that physically pushes your car. Use it to regain speed quickly after a crash or to correct your direction when exiting a corner. Need For Speed - Most Wanted 5-1-0
For a complete list of all 15 rivals and their specific race requirements, you can refer to this Full Event Guide . Need for Speed: Most Wanted 5-1-0 - Guide and Walkthrough You must defeat 15 rivals to reach the top