Yeah, I get that - but that is a flavor description. If I wanted to change the flavor description for my version and make it related to social skill instead, do you have a suggesting for raising the DC?
Hmm. In that case I'd say Will saves work out well, possibly with synergy bonuses for Diplomacy or Knowledge (Demonology).
If it's social-based, I'd change the mechanic a little and actually apply the spirit's rating on the
first roll, because you're haggling with the spirit, not cramming it in your body.
Given that, I'd almost change the mechanic by which the difficulty ramps up as well. Give it more emphasis on what spirits will get along with what other ones. So for example if you're petitioning a spirit whose ethos jives with the ones you've already petitioned, it's just the spirit's rating that's the penalty to the roll. If you're petitioning a spirit who's less cooperative, the penalty is both its rating plus the ratings of any spirits you've petitioned who oppose it. It's a social or will roll, so you're actively
convincing the spirits to work together.
I can't think of a quick and dirty way to make the math work on that one. Maybe use what domains the spirit has to calculate it. Give each domain an opposing domain on a chart, and say that one opposing domain gives the spirit's rating in penalty, and two opposing domains means the match is completely incompatible.
It's something that now that I think of it, I might include in the Shaman, as it's easier than all that "so-and-so will not walk with whatsisface" dealie. I was basing those off of the actual animal spirits, but basing it off of domain means you can make spirits up much more quickly.