I'm painfully aware of some math I am doing wrong when building monsters using Realms of Power: Magic, but not quite sure what the right answer would be.
First of all, what determines the Soak score of a supernatural being? There are Qualities that can increase and decrease the Soak score, so it is unlikely to be completely arbitrary, and some semblance of balance is required for player character creatures. I can't seem to find the math in RoP:M, ArM5 core or anywhere else.
Second is a much easier question; which Characteristics increase or decrease the stats on a weapon or unarmed attack? I could not help but notice that the example serpent in RoP:M has an Attack accuracy of +7 on its fangs, despite its fairly low Dexterity.
Everything should be a product of the equations on p171 of the core book modified by the virtues, flaws, and qualities that are relevant. The weapons for creatures are found on page 43 of HoH: Mystery cults. If you don't have that book a lot of natural weapons can be found in the book of mundane beasts here: atlas-games.com/pdf_storage/ArM5Beasts.pdf
They took the natural weapons section out of the write ups in RoP Magic. Don't know why.