Slumbering Mu Spore

From the introduction: Two Demon Lords have trapped and subdued a giant Mu Spore deep in the great forest. While the Drow minion of Haagenti, Demon Lord of Alchemy, keep the monster alive but asleep, the minions of Zrl'Zug, Demon Lord of Fungus, work to complete a ritual to convert the creature into a half-fiend fungal war machine. The conversion will be complete in three days, at which point the Drow and fungal creatures will have a sentient, flying siege weapon to crush the Elves of the forest.