Mobility

The sooner you hit it, the faster you're still going. I dunno why it works like that but that's how it seems for me.

Inertia and friction. I know I'm applying Physics to Nexon's creations, but it does make sense here.
If you FJ in one direction and keep hopping up after you land, you'll notice the Inertia part. I do this to throw stars at my back's direction while still moving forward. (Jump, FJ, turn around, jump again when you land, throw star while flying forward with inertia, rinse and repeat upon landing)
If you do a single Combat Step, you'll move slower over time and stop at one point, that's friction.