Let's say the party is fighting a high HD orc priest and his unholy mutant cthuloid monsters --The orc is under the spell Hold Person, but the following round, he's rescued by another orc and their crocodile/giraffe hybrid. (it's a giraffe with crocodile mouth, and long spiked tail (and cathulu-monster-eque eyes all over its skin instead of spots).
This thing picks up the Held chieftain and rises to its full height ready to run away. The party has a chance to act before it does run off.
So orc guy is out of melee range, but for missile attacks and Spiritual Weapon... what to hit bonus do you suggest? if he was Held, and not moving on the ground, I'd say hit automatically (though there is a berzerk fire-breathing elephant with it's front legs tied together jumping around, so that qualifies a "battle chaos" and I suppose that means everyone should roll to hit...) But I figure being Held makes you helpless, so automatic hits, before the rescue attempt.
I think using the giraffe's AC would be too generous since the giraffe monster isn't necessarily actively defending the orc, but it's massive mouth is some cover, and it's alive and well, ready to run off.
(certainly the orc would lose any Dex AC bonus, if C&C had such, because of Hold Person, or 3e probably has a rule for it).
I plan on using the orc's real AC and just adding bonus to the party's To Hit (rather than AC penalty to the orc... it's 6 of one and half a dozen of the other, but still it seems easier to wrap our collective head around).
The cleric's player suggested +10 to hit since the orc is held and helpless. Off hand I feel like that might be too high. The monster is moving and whatnot, and nothing stays still waiting it's turn in initiative.
SO, long question short: What bonus (if any) would you give the player's to hit the Magically held orc, held aloft in the tall monster's mouth? 
