Sibat wrote:
This weapon is similar to a shortspear with a flexible rattan or bamboo shaft and an elaborately barbed head. On a critical hit, the spear grabs flesh or armor. The wielder can then attempt a combat maneuver check to attempt to grapple its opponent as a free action. This grapple attempt does not provoke an attack of opportunity from the creature you are attempting to grapple. While grappling the target with a sibat, the wielder can only move or damage the target on its turn. The wielder is still considered grappled, though it does not have to be adjacent to the target to continue the grapple. If you move far away to be out of the sibat's reach, you end the grapple with that action.
So as far as I can tell:
1. If you crit with the sibat you can make a combat maneuver check (this is the only time you can use it to grapple). This uses your CMB plus any bonuses to using your sibat (weapon focus, +4 weapon, etc.).
2. Same bonuses as you used to make the initial grapple (plus any bonus for maintaining it). You can only choose to move or damage though.
3. With grapple your combat maneuver check is your "attack" roll. If you succeed on the grapple check you just automatically do damage.
4. So this one is going to take a much longer explanation, and include the answer to pinning from question 3. If you are grappling using the sibat you can only move or damage. In order to pin them you would need to grapple them normally. The most conservative reading would require that you drop the grapple and re-grapple them if you wanted to pin them, but it also seems reasonable to allow you to maintain while not including the sibat bonuses to make a grapple check to do something other than move or damage. In general, you cannot maintain the grapple on the same round you initiate it (it specifies subsequent rounds). So you cannot initiate a grapple and make a grapple check to pin in the same round with Greater Grapple. But it's important to note, you can't pin at all if you're using the sibat.
