While Parsimony does reduce how much MP is used after casting, it does not reduce the cost before casting.Parsimony: Reduces MP cost of next attack spell by half, and restores MP when spell is cast.
Lets say you have a spell that costs 500 MP. And you only have 250 left.
Casting the spell would only cost 250 MP, but you are unable to cast it unless you have 500 MP left.
I hereby request for this to be changed so that Parsimony reduces spell cost before casting.
Like this if you'd like to see this.