Dragon Age: Ascension
Incredibly rare alchemical ingredient.
An ancient and extremely rare substance that can only thrive where the sun cannot reach. It glows a sickly pale green and is kept safe by a Guardian Serpent.
The party discovered that the firesprites feed off of it to survive, and that one of the creatures becomes the Guardian Serpent each generation. They were forced to slay the beast and retrieve the shadowmoss in order to save Sothmere, most likely dooming the firesprites to extinction.