This is a response to Monsters and Manuals
WizardKnighting Planescape - where he posits an alternative Planescape with mechanics better reflecting the ability and imperative to shape the planes.
Read it all, it is good stuff, but the relevant piece for this is
"In Planescape, one of the idealised things that PCs are supposed to be doing - it is suggested - is reshaping the planes through their actions [or] by acting in the name of a God (although the writers called these 'Powers') of one kind or another, they can literally physically enlarge his or her sphere of influence. And, of course, the PCs can themselves aspire to ascend to Godhood and carve out a realm of their own, individually or collectively. [...] There is an unwritten but much better version of Planescape out there in the ether, in which PCs' stats are largely to do with belief and values, and they roll against these stats in order to effect change in their surroundings."
This is a very interesting take - I agree with the critique in that the setting and a bunch of the adventures made it clear that such things should be happening - Recruiters in Well of Worlds is about exactly that. Sig
My immediate reaction to 'other stats about belief and values' is to think of
Spire/Heart. There Dark Elfs start a revolution with all the different stats like wealth, blood, magic to stress to get things done. For this ether-Planescape it could be belief (strength thereof), alignment, might, whatever - a bunch of stats that would fit to different circumstances to stress/flex. Playing Spire for me it took a lot to get away from 'I hit it' to 'stress silver to just pay the guy to look the other way' but once I got into the groove it gave a much better sense of getting things done without going blades drawn all the time.
Spire had stats of -
Blood: Physical damage and exhaustion.
Mind: Mental stress, instability and insanity.
Silver: Loss of money or resources.
Shadow: Loss of secrecy, damage to cover identities, police and government attention.
Reputation: Loss of social standing in a group or community.
I like the range there, lots of different ways you can get burnt, which I would like to flip to become what are the many ways that one can mystically affect the planes.
Sig, City of Blades is nominally a Blades in the Dark refit of Sigil that is kind of the right system in kind of the right setting but is not looking to achieve the effects we want - it does have the stress system but it is focused on personal prowess, kinetic action and the like - not this more cosmic, warping of realms idea.
My initial thoughts are on a model with axis of matter/mind and dominating/persuasive:
Strength of Will = push through resistance, shape the stuff of a place around you like a cloak
Arcane Cunning = twist to shape, recognise the threads of fate and pluck and tease them to your preference
Belief = resonance, pull others to your vision, be as a beacon
Dreamworking = envision the thing and convince others they perceive it too