I like this, it gives another element a way to remove poison (darkness way, of course!).
The card is balanced and doesn't really need other work, imho.
If i can suggest a thing on the flavor side, i'd like to see this as a really crude chirurgic operation, that removes poison but damages in the process. Maybe this could be a voodoo sanctuary/laboratory, since Darkness already has voodoo! I did a quick research, and found that voodoo temples are called Hounfor, Ounfo, Hunfor (i think there are many translitterations).