Use the Bottled Bileberry Brew on the corpse of a Twilight Inferno Lord, then speak with him.
The potion you created is vile enough to wake the dead. Which is its intended purpose.
Slay a Twilight Inferno Lord and force the brew down his throat. He will revive, if only briefly, and be completely under your dominance.
Speak with him and learn the true name of the fire elemental he is channeling into the world to burn down your precious forest.
Also, you get: 3 90
<The wretched creature before you speaks in a wavering voice, its body broken but briefly animated by Blackhorn's vile potion.>
Upon completion of this quest you will gain: