Black Core - Basically a fuel source and magic type that could have it's own effects.

It would be nice if for useage, you can throw it in a Bonfire, like people suggested, but instead, use it to light a Bonefire, or make a special kind that is more gothic or sinister looking that causes a fear debuff to most normal or simple creatures. This would scare off anything from normal wildlife like Deer, Wolves and Boars, to Necks, or maybe even Trolls, or Fulings if you had a good idea of what would be balanced and the theme of the biome.