What about it being a Faerie skill that uses Faerie Gauge? It's a toggle, and then if you run out of Faerie Gauge it starts to eat at your MP like Lost Font of Magic. It'd give the Gauge a bit more of a purpose as well as add two things of management to think about. I kinda like that idea, though by then it's not Miasma 2 anymore, but something new.
But yeah, sounds fun.