from Rules of the Game - Unarmed Attacks (Part 2)
Unarmed Strikes and Natural Weapons
Just as a creature can add weapon attacks to a full attack made with natural weapons, so too can it combine unarmed attacks with natural weapons. Two options are available to accomplish this task.
A creature can choose to treat its unarmed attacks as its primary attacks and its natural weapons as secondary attacks. (This method is normally used to add weapon attacks to a natural attack routine.) The creature must make all unarmed attacks with its primary limb, which prevents that hand from being used for a natural attack such as a claw or slam. It uses its full base attack bonus for the natural attack, gaining additional attacks as normal for a high base attack bonus, and adds its full Strength bonus on damage rolls. Of course, each of these attacks provokes an attack of opportunity if the target is unarmed (unless the creature has Improved Unarmed Strike). However, its natural weapons all become secondary attacks, taking the -5 penalty on attack rolls (or -2 with the Multiattack feat) and adding only half the monster's Strength bonus on damage rolls.
A simpler method is to treat the creature's unarmed attack as an off-hand attack. (After all, an unarmed strike is rarely as effective as a weapon attack would be, so it doesn't really merit the same level of priority in the average monster's attack array.) Instead of using its primary limb to deliver the unarmed attack, it uses a kick, head butt, or other appendage that isn't otherwise used to deliver a natural attack. The creature gains one unarmed strike, which deals damage appropriate to its size plus half its Strength bonus (since it's an off-hand attack). A creature using this method suffers a -4 penalty on all attacks (since it's effectively fighting with two weapons and its off-hand weapon is light). The damage for its natural attacks is unchanged. This method requires fewer calculations on the fly, so it's probably easier to use in play.
Let's look at the nalfeshnee for an example of how each of these methods would work in play.
A nalfeshnee using the first method would have three unarmed attacks (thanks to its base attack bonus of +14). Applying its size modifier, and Strength modifier, the nalfeshnee's total attack modifiers for its three natural attacks are +19, +14, and +9. These natural attacks each deal 1d6+7 points of nonlethal damage. Each of the nalfeshnee's natural weapons takes a -2 penalty for a secondary natural weapon (thanks to the nalfeshnee's Multiattack feat) and gains only half the nalfeshnee's Strength modifier to damage, which gives it two secondary attacks, as follows: one bite +18 (2d8+3) and one claw +17 (1d8+3); it loses one claw attack in order to make unarmed attacks with its primary limb.
Using the second method, the nalfeshnee's natural attacks are made at a -4 penalty (bite +16, 2 claws +13) but deal normal damage. It then makes one unarmed attack at +15 (+14 for base attack bonus, -2 for size, +7 for Strength, -4 for off-hand light weapon) that deals 1d6+3 points of nonlethal damage.
