Place a fan in the middle of a big space in Toybox mode. Next, place a ground-type vehicle (you can use a power disc and ride a vehicle, if necessary). Next, drive the vehicle up to the fan and nudge your way forward so that the air current from the fan lifts you and holds you aloft. Perform back or front flips at your leisure, and then drive off and land on the ground safely for a bunch of easy XP.