Wings of Redemption
A levitating creature that attacks with a melee or ranged weapon finds itself increasingly unstable; the first attack has a -1 penalty on attack rolls, the second -2, and so on, to a maximum penalty of -5. A full round spent stabilizing allows the creature to begin again at -1.
Note: If a creature ends up on the ceiling in Reverse Gravity, they are essentially on the “ground” and thus can move normally (though watch out when you get to the edge!) and avoid this penalty. The penalty applies only while oscillating freely at the top of a Reverse Gravity field.