…that being said, even though I found solutions (because I had to!), any input from fellow GMs about how to solve the monster-to-NPC conversion issues are welcome. So, I'm creating a Major Great Spider (C&T) NPC, with the ability to shapeshift into a human being (well, she looks like one, at least, since her internal alchemy is hardly human…), giving her a full character sheet, with stats, a profession, skills, etc.
How would you go with it?
There are many (many!) issues.
First, the level. Since RM2 creatures' levels are absolutely not tied to either their OB, HPs or spellcasting abilities (some creatures have a low level, yet an absurdly high OB, some are the opposite, some know spell lists to a higher level than their own, some to a way lower level, not to mention weird PPs calculation sometimes above 3 PPs per level), it's very hard giving one an actual level when giving it a character's sheet.
Then, the profession. Because of the above, regardless of the profession you give a creature, many things are very wrong when you compare the result to the basic C&T creature. Too many or not enough HPs, PPs, spell lists, etc. Spell-using professions have it even worse with the basic C&T creature sometimes having spell lists from at the same time base spell lists (from several professions even!), open and closed lists from different realms!
At last, the stats. It's just a nightmare to give racial stat bonuses, even with the help of the RoCo. VI.
Anyway, so, I used the spider hengeyokai in the OC as a basis, and altered the bonus stats with the help of the RoCo VI, since in my opinion the spider hengeyokai are more based on the Greater Great Spiders rather than the Major ones. I also gave her a level lower than the basic C&T one, to compensate with the fact she'd, as a character with a true profession, actually have more spell lists. Etc.
How would you do, if you were in my position?