You will earn this when you complete the final rank "Barry" and choose "Cash In" to start over again. Missions are fairly random and can be any of the following:
Reach a set distance
Run x amount of distance on foot
Rub your head on the roof for x amount of distance
Reach x amount of distance without touching the roof or floor
Reach x amount of distance without using the Machine Gun Jetpack
Reach x amount of distance without using a vehicle
Reach x amount of distance without harming any scientists
Reach x amount of distance without collecting any Coins
Reach x amount of distance in any vehicle
Reach x amount of distance in a certain vehicle
Run/fly x amount of distance in a certain vehicle in a single run
Collect x full groups of coins
Collect x amount of coins in one game
Collect x amount of spin tokens
Collect x amount of spin tokens in one game
Destroy a certain vehicle x amount of times
Purchase and use a Final Blast
Purchase and use a Head Start
Purchase and use a gadget (If already purchased, just use it for one game)
Purchase an item from The Stash
Have a near miss with a Missile x amount of times
Have a near miss with a missile x amount of times in one game
Have a near miss with Zappers x amount of times
Have a near miss with zappers x amount of times in one game
High five x amount of scientists
High five x amount of scientists in one game
Brush past x amount of red flashing lights
Brush past x amount of red flashing lights in one game
Zigzag past x amount of zappers
Collect x amount of groups of coins
Fly over x amount of zappers
Play x games
Each mission is worth a certain number of stars (1, 2, or 3) that you will earn towards your rank when you complete it. Here is a list of the ranks and how many stars you need to complete each:
Beginner: 3
Learner: 3
Rookie: 3
Novice: 5
Amateur: 5
Graduate: 7
Skilled: 7
Experienced: 7
Professional: 9
Hotshot: 9
Expert: 11
Wizard: 11
Ninja: 11
Super Star: 13
Barry: 13
Also, if you ever find yourself struggling with a tough challenge, you can skip it by going to the Utilities menu and paying 5000 coins for a 1-star mission, 10000 for a 2-star, or 15000 for a 3-star. The mission will automatically be completed and you will earn the stars for it.