Why? Putting characters i like vs each other lol. Guessing this is my surprise.
As op is demiurge is, her biggest weakness is she can't deal with people like herself who have mid-godly regen, she has no concept manipulation or sealing.
M on the other hand has sealing, and considering he is the king of a race of conceptual beings, and fodder in comparison to him like Golden King can kill conceptual beings, safe to say he can kill ppl with mid-godly, he is also a conceptual existence, and is everything within sharnoth, a place which has infinite darkness, and that only exists because he has no emotions.
Anyway demiurge can't deal with M's regen, and M can kill or seal demiurge, however now that i think about it demiurge still has phantasmagoria which is mind manipulation + empathetic manipulation + illussion creation. M has no resistance to those and while it would be absurd to think a critter like say
Bandersnatch could mind hax M, their mind hax only works on like 1 person while demiurge's works on entier cities, also still would be the issue of the empathetic + illussion manipulation.
Damn, hmm the precog might give demiurge an edge here again, if she sees and knows everything about M, she could incap with phatasmaoria, unless i am missing some resistance to that that M has.