You know, it helps if you click "Save" after typing an update.
Rather than the "An ihagnim can try to devour a grabbed opponent of a smaller size than itself by making a successful grapple check" I'd prefer it if the Ihagnim could devour a Large creature, i.e.:
Devour (Su) Swallowing #2: An ihagnim can try to devour a grabbed opponent its own size or smaller by making a successful grapple check. Once devoured, the opponent is consumed in 1 round. The ihagnim destroys the victim's body and prevents any form of raising or resurrection that requires part of the corpse. There is a 50% chance that a wish, miracle, or true resurrection spell can restore a devoured victim to life. Check once for each destroyed creature. If the check fails, the creature cannot be brought back to life by mortal magic. A devoured creature can cut its way out by using a light slashing or piercing weapon to deal 20 points of damage to the ihagnim's interior (AC 20), but only have 1 round to escape before being consumed. Once the creature exits, the ihagnim's flesh closes the hole; another devoured opponent must cut its own way out.
An ihagnim's interior can hold 1 Large, 4 Medium, 16 Small, 64 Tiny, or 256 Diminutive or smaller opponents.
Devour (Su) Engulfing #2: An ihagnim can try to devour a grabbed opponent its own size or smaller size by making a successful grapple check. Once devoured, the opponent is consumed in 1 round. The ihagnim destroys the victim's body and prevents any form of raising or resurrection that requires part of the corpse. There is a 50% chance that a wish, miracle, or true resurrection spell can restore a devoured victim to life. Check once for each destroyed creature. If the check fails, the creature cannot be brought back to life by mortal magic. Devoured creatures are considered to be grappled and trapped within the ihagnim's body. They have one round to escape or kill the ihagnim before being consumed, and can only use light slashing or piercing weapons to attack its interior (AC 20).
An ihagnim's interior can hold 1 Large, 4 Medium, 16 Small, 64 Tiny, or 256 Diminutive or smaller opponents.
I'm also wondering whether we should reference the 30 cubic foot capacity of a
bag of devouring in the ability, maybe by making the final paragraph "An ihagnim's interior can hold 1 Large, 4 Medium, 16 Small, 64 Tiny, or 256 Diminutive or smaller opponents, or up to 30 cubic feet of material."?