From time to time, I'll try my hand at making new monsters. When I do, I'll usually follow the rules in the Bestiary pretty closely, as that seems like the best way to come up with a creature that meets its target CR.
One of the rules I follow pretty closely therefore is the table denoting natural attack damage values by size. In other words, the damage dice for given types of natural attacks for creatures of various sizes is set according to this table (and the Improved Natural Attack feat).
Lately, however, I've started noticing monsters with natural attack damage dice far in excess of their size. The pit fiend, for example, is a large creature (and has no instances of Improved Natural Attack), and so should have attack/base damage dice as follows: claws/1d6, wings/1d6, bite/1d8, and tail slap/1d8.
Instead, its damage dice are claws/2d8, wings/2d6, bite/4d6, and tail slap/2d8. In other words, it's had all of its natural attack damage dice bumped up quite a bit.
My question then is if the table for natural attack damage is not so much an actual rule as it is a guideline? Do some monsters naturally get better damage values without a rules notation (the way there is for dragon's bite attacks, which is about Strength bonus to damage, rather than damage dice), or are instances like the pit fiend in error?
