reveal said:
I usually take size into consideration. For example, if a Medium size enemy is grappling a Medium sized PC, there's a 50% chance to hit PC. If a Large size enemy is grappling a Small sized PC, I'd probably say around a 10-15% chance to hit the PC.
My houserule is to use a system where the smallest creature is 1 and each size category higher is double that. Then, the chance is rolled on a die equal to the total (or larger, rerolling invalid numbers). So, if two medium creatures were grappling a large creature, then I'd roll a d4 and on a 1, hit one medium creature, on a 2 hit the other, and on a 3 or 4 hit the large creature. If one of those medium creatures were a small creature, then I'd roll a d8 and on a 1 hit the small creature, on a 2-3 hit the medium creature, and on a 4-7 hit the large creature, and reroll an 8. It's not too complicated and works well for those extremely rare cases when someone fires a ranged weapon (or spell) into a grapple.
A few questions of my own:
1. A creature with improved grab who took a -20 penalty is not grappling, so you do not roll randomly to hit such a creature. However, do you roll randomly to hit the victim of such a grapple? Consider the case where a spellcaster's summoned monster grapples the party fighter with improved grab at -20. If the spellcaster wants to hit the fighter with a ray spell, does he have a chance to hit his monster?
2. When you grapple, you move into your opponent's space, or you pull your opponent into your space (improved grab). Does this actually imply you share the space or, say in the case of a medium creature and a large creature, does the medium creature only occupy one of the four squares of the large creature's space? Who's option on which square?
3. Can you squeeze while grappling, or forced to be squeezing while grappling?