Bah, and wht of those twins who share a body below the waist, hmm? what of them?
actually, perhaps two human brains in a body wold resist demonism more strongly?
Make a hidden "control points" stat, to determine how many alterations, and how much demonism, one human mind can control. Then, I could see additional human arms and the like costing less overall than, say, a spiked tentacle of crushing. but there would be a limit, or perhaps make it a matter of diminishing returns.
But seriously, check out my previous comment. I am interested in your feedback on that idea.
Power level as the second stat could work, but it also means effectively limiting things to an action of some power level and a passive effect. I can slash with power 3 and I have a passive bonus to slashing attacks.
It is completely functional but also no where near as interesting as the "Functional and structural" approach we're working on now. Namely because it is limited to the 5 body lines that I pre-established; you can't easily expand the system in neat ways and I fell like it will lead to part favoritism because almost everyone will just try to get the most high powered part.
Character growth = growing extra limbs.
end game = Literal Human centipede
This is actually a really good idea in a way.
Earlier I said that leveling up would entail eating enough parts of a particular stat to level it up. But thats a lot of book keeping. Instead, we could work it like this:
When you level up you can choose from between three rewards.
1. Permanent boost to some stat. Totally independent of your body make up. Call it leveling up your soul or something.
2. Permanent boost to the amount of humanity human parts provide. Effectively this allows you to have less human parts and still maintain the same regen of humanity.
3. The formation of a new "Normal Part Slot". If we look at our standard body and say we have a central body with three parts (gut, chest, head) and then 4 limbs with 3 slots each, then it becomes easy to say "Ok, well I want to expand the central body to be 4 slots. Or I want to expand the left arm to be 4. Or I want to add an entirely new single slot limb." And the idea is that, while you can add parts to yourself whenever you want, parts in these slots will not cost against as being "Extra" and drain more Humanity. So you could theoretically just expand your slots and have many extra human parts without taking any humanity penalty.