MotoGP 08

The exact Scenario challenges are numbers: 3, 9, 12, 14, 19, 22, 26, 35, 38, and 43. Most of them require you to complete the previous challenge; you will see the requirements to unlock the challenge in the description.

If you press Y at the list of challenges, you will come to the Riding Model screen. Make sure you have Arcade Riding Model and Automatic transmission to make the challenges a lot easier.

3, 14, 22, 26, and 38: Have to finish 1st.
9 and 43: Have to finish 3rd or higher; and #43, you can never get passed.
12: Have to finish 5th or higher.
35: Have to finish 6th or higher, and never get passed.
19: Have to finish 16th or higher.

I think it's worth noting that I didn't unlock this achievement until I completed all of the 1vs1 challenges also.

Somebody please correct me if I am wrong, but I believe this achievement is glitched. I have personally completed all of the challenges, but the last one is just a picture and will not check off.