In my world, similar to our earth, a person has the ability to create gravitational "spheres".
- modify its location
- vary the force
- move the sphere (once created)
- select what or who is affected by this sphere
For example if he creates a sphere next to an item, he can move it (like telekinesis) or if he is on a skateboard, go up a hill like if he was downhill with a sphere strong enough always in front of him. Even fly?
My question is, how could I limit his power? Apart the progression level his ability gain, like first small sphere, then more powerful ones, what weaknesses would he have?