When binding a water elemental, it says if you surround it with fire when first summoning it, you can make an opposed will check to gain control quickly. The only problem is, I can't find any other place in the game where "opposed Will check" is called for, nor any info on what exactly is used for this check (Wisdom score? Add your Will save bonus?)
How does this work?
I guess that you are asking about opposed Charisma check that is part of using planar binding spells.
If the creature does not break free of the trap, you can keep it bound for as long as you dare. You can attempt to compel the creature to perform a service by describing the service and perhaps offering some sort of reward. You make a Charisma check opposed by the creature's Charisma check. The check is assigned a bonus of +0 to +6 based on the nature of the service and the reward. If the creature wins the opposed check, it refuses service. New offers, bribes, and the like can be made or the old ones reoffered every 24 hours. This process can be repeated until the creature promises to serve, until it breaks free, or until you decide to get rid of it by means of some other spell. Impossible demands or unreasonable commands are never agreed to. If you ever roll a natural 1 on the Charisma check, the creature breaks free of the spell's effect and can escape or attack you.
Nope, the entry calls for an opposed Will check, which if you succeed gives you a +4 to the opposed Charisma checks. Only place in the game I can find that asks for an opposed Will check.
Ah, you are refering to Ultimate Magic "Binding Outsiders" section.
*reads*
Well, it is rather self-explanatory (at least prd version). The opposed Will check is not made to gain control but to distract the elemental long enough to gain bonus on opposed Charisma check I mentioned: the caster starts fires around magic circle, conjures water elemental and then both the caster and the water elemental make a Will saves. Caster gains bonus for each fire present. If the caster's result is higher then he gets +4 bonus to Charisma check. Needless complication on the designer part comparing to binding other elementals where using appropriate materials just grants the bonus without need for additional non-standard checks.
Ok, thanks.
If you are GM I suggest dropping the opposed Will check and just grant the conjurer +1 to +4 bonus to Charisma check depending upon the size of fire and quality/cost of fuel.