I'm confused though, what makes it different from say, feyfire which I can use without the required magic material?

Hello @skaz88,
The unlock condition for Ghostfire damage is indeed a custom requirement which is likely out of reach of the mod you're using.

I think something is up with ghostfire, I'm using a mod that unlocks every infusion and it works for eveything you've added, even the new damage types, except ghostfire.