Disable gravity for a single dynamic object in the BGE? I have a sphere which I use to restore dynamics on objects it collides with (by expanding to cover the shards over the course of the animation); the collided objects are "shards" of a crystal, and the sphere is a ghost so it does not affect any part of the crystals except the state of their dynamics. I have a collision node set to detect collisions with the material of the sphere, but that requires it to be a dynamic object.

I need to make the sphere unaffected by gravity during physics simulation, since there is no way to set the mass to zero, and collisions will not be detected with static objects. 

This question has a similar problem, but setting the sphere to a character simply made it glitch out and not expand correctly.
In order to make an object "not have" gravity, you can move the object up at the same speed gravity pulls it down.

Connect an Always sensor to an And controller and this last one to a Motion actuator, with a value of 9.8 * mass (where mass is the value for Mass, set in the Physics tab of the Properties window) for the Z axis.