This requires 2 things:
A Fan and A Stunt Buggy ( Any car will do, Though the stunt buggy helps more due to its wheels )

• Place the fan down anywhere preferably somewhere with alot of space.
  
• Place down a stunt buggy.
  
• Enter the stunt buggy and slowly approach the fan.
  
• If you cant move anymore forward just jump and you will be flying.
  
• Then do Alot of flips holding down shift and W or S works on keyboard, I think on the controllers its the other thumbstick to moving around.

Every 5 minutes or so hop off of the fan by moving to one of the sides and hop back on until you have leveled up your character, once they are level 15 they are maxed and they wil have a gold statue in the hall of heros.
Thanks for reading.