I'd be amenable to that idea.
Revising...
Shatter Bone (Su): Four times a day, a visceraith can try to shatter a limb-bone or jaw-bone of a single opponent within 60 feet. Shatter bone cannot affect boneless creatures, but can harm creatures whose skeletons are made of chitin rather than bone, such as most vermin. The opponent must succeed on a DC 16 Fortitude save or suffer compound fractures in the targeted bone, which inflicts 2d6+4 damage. The round after the bone is shattered the opponent takes an additional 1d6+4 damage.
In addition to the damage, a shattered bone imposes the following penalties: a body part with a shattered bone lacks the Strength to hold and carry objects or make attacks, held items are dropped, but worn items are not dropped; if a shattered limb is used for locomotion (for example, a leg), the target's speed drops by three-quarters and Dexterity suffers a -8 circumstance penalty; if a shattered limb is used for manipulation (for example, an arm), the target's Dexterity suffers a -8 circumstance penalty and all spells with somatic components require a Concentration check (minimum DC 15); a target with a shattered jaw bone suffers a -8 circumstance penalty on skills checks requiring speech and all spells with verbal components require a Concentration check (minimum DC 15). The save DC is Charisma-based.
A shattered bone normally takes Z days to heal naturally (half that time if DC 15 Heal checks are used to provide long-term care), but can be instantly cured with a restoration or higher-level healing spell.
Alternatively, instead of secondary damage we could honour the 2hp/round by having a shattered bone do 1d4 damage when the victim makes a move or standard action, with a Fort save to negate?
Something like:
Shatter Bone (Su): Four times a day, a visceraith can try to shatter a limb-bone or jaw-bone of a single opponent within 60 feet. Shatter bone cannot affect boneless creatures, but can harm creatures whose skeletons are made of chitin rather than bone, such as most vermin. The opponent must succeed on a DC 16 Fortitude save or suffer compound fractures in the targeted bone, which inflicts 2d6+4 damage. Whenever a creature with shattered bones makes a move or standard action, it must succeed at a DC
X Fortitude save or take an additional
1d4 damage. The Fort DC and damage increases by +1 for each extra limb or jaw bone that is shattered (e.g. DC
1d4X+2 and
1d4+2 for three shattered bones). A DC 15 Heal check can immobilize a victim's shattered bones and prevent this additional damage.
*rest the same*
