I think it was +Patrick Stuart who wrote a nice set of new narrative magic rules suitable for pbtA-like games. We use them in lieu of the existing WoD magic rules.
They’re deceptively simple.
You cast a spell. Name it, describe it and give your intended effect. Roll + INT. On a 10+ chose 3, on 7-9 choose 2.
– There is very little blow-back.
– It has roughly the intended effect.
– Nothing unbelievably weird happens.
– There is no damage to your memory.