OK. I gathered up what we've got so far:
Control Gravity (Sp): At will, Crius can produce an effect like that of a reverse gravity spell (caster level Xth; Reflex save DC X), except that the range is X feet and it affects an area of up to X 10-foot cubes. Crius simply stacks the cubes to reach a ceiling or other overhang, then uses any remaining area to disrupt the prey's companions.
Alternatively, Crius can increase the gravity in an area. Creatures within the area must make a Will (?) save or be pulled downward. Airborne creatures are pulled downward and reach the ground in 1 round. Falling objects and creatures take falling damage as normal.
Lifting an object in this area is difficult; treat all objects as weighing X times their normal weights.
Thrown weapons are ineffective within the heavy gravity field, even when launched from outside the field. Attacks with other ranged weapons take a –2 penalty on attack rolls for every 5 feet of the field’s area they pass through, in addition to the normal penalties for range. Slashing and bludgeoning weapons suffer a -2 on attack rolls and only do half damage. Any creature attempting a grapple check suffers a -2 on the check.
A successful Climb check lets a creature move one-quarter its speed as a move action or one-half its speed as a full-round action.
Freedom of movement negates all penalties and allows normal movement.
Alter Weight (Sp): Crius can also change the weight of a single object as a standard action. Crius must have line of sight to the object he wishes to affect. He can make the object either weightless, causing it to float upward as per the reverse gravity spell if unattended. Alternatively, he can increase the weight of an object, making it too heavy to lift for 1d4 rounds.
If Crius concentrates on an object for 1 minute, he can permanently change its weight. If he chooses to make the object too heavy to lift, nothing short of a wish or miracle spell can allow the object to be lifted.
We still need to figure out the effect on encumbrance, which effects movement and armor check penalty.
I also found the following information in the "Planes" portion of the SRD (culled from the new DMG and MOTP). I don't know why I didn't remember this earlier! :\
Gravity: The direction of gravity’s pull may be unusual, and it might even change directions within the plane itself.
Normal Gravity: Most planes have gravity similar to that of the Material Plane. The usual rules for ability scores, carrying capacity, and encumbrance apply. Unless otherwise noted in a description, it is assumed every plane has the normal gravity trait.
Heavy Gravity: The gravity on a plane with this trait is much more intense than on the Material Plane. As a result, Balance, Climb, Jump, Ride, Swim, and Tumble checks incur a –2 circumstance penalty, as do all attack rolls. All item weights are effectively doubled, which might affect a character’s speed.
Weapon ranges are halved. A character’s Strength and Dexterity scores are not affected. Characters who fall on a heavy gravity plane take 1d10 points of damage for each 10 feet fallen, to a maximum of 20d10 points of damage.
Light Gravity: The gravity on a plane with this trait is less intense than on the Material Plane. As a result, creatures find that they can lift more, but their movements tend to be ungainly. Characters on a plane with the light gravity trait take a –2 circumstance penalty on attack rolls and Balance, Ride, Swim, and Tumble checks. All items weigh half as much. Weapon ranges double, and characters gain a +2 circumstance bonus on Climb and Jump checks.
Strength and Dexterity don’t change as a result of light gravity, but what you can do with such scores does change. These advantages apply to travelers from other planes as well as natives.
Falling characters on a light gravity plane take 1d4 points of damage for each 10 feet of the fall (maximum 20d4).
No Gravity: Individuals on a plane with this trait merely float in space, unless other resources are available to provide a direction for gravity’s pull.
Objective Directional Gravity: The strength of gravity on a plane with this trait is the same as on the Material Plane, but the direction is not the traditional “down” toward the ground. It may be down toward any solid object, at an angle to the surface of the plane itself, or even upward.
In addition, objective directional gravity may change from place to place. The direction of “down” may vary.
Subjective Directional Gravity: The strength of gravity on a plane with this trait is the same as on the Material Plane, but each individual chooses the direction of gravity’s pull. Such a plane has no gravity for unattended objects and nonsentient creatures. This sort of environment can be very disorienting to the newcomer, but is common on “weightless” planes.
Characters on a plane with subjective directional gravity can move normally along a solid surface by imagining “down” near their feet. If suspended in midair, a character “flies” by merely choosing a “down” direction and “falling” that way. Under such a procedure, an individual “falls” 150 feet in the first round and 300 feet in each succeeding round. Movement is straight-line only. In order to stop, one has to slow one’s movement by changing the designated “down” direction (again, moving 150 feet in the new direction in the first round and 300 feet per round thereafter).
It takes a DC 16 Wisdom check to set a new direction of gravity as a free action; this check can be made once per round. Any character who fails this Wisdom check in successive rounds receives a +6 bonus on subsequent checks until he or she succeeds.
